Ian's hyper-curated, eco-passive, kind-of-crunchy, not-at-all-miniature, but as-condensed-as-she-could-make-it, life guide.

This is going to be such a wall of text... Good luck!

General life

Buy it once, keep it forever.

Longevity! Wherever possible, it's best to buy a reusable version of things, like cloths over paper towel, menstrual cups over tampons, or safety razors over disposables. Obviously, this disposable stuff comes with the issue of landfill and rubbish, and of wasting materials and energy on making junk. Sure, you can recycle stuff, but that costs more energy again. Better to never have it. Before you retire things, see if you can repair (or get someone else to repair) them! Clothes are easy, shoes are easy, furniture and tech can be easy. Extend their lives and always keep shoe-goo in your junk drawer. I am a firm believer in the household tool box and sewing kit. If you do end up having to retire it, repurpose it! There are always places for things to go, either to other people, or in your own home. I like to buy things that I know I'll be able to repurpose later when I do have to buy temporary objects, like getting the toothbrushes with the flat handles instead of the round ones. I turn them into plant pot markers once I retire them. Reduce, reuse, recycle type beat.

The 'gifted, thrifted, rescued, clearance' approach.

Where it makes sense to (for me that's clothes, furniture, homeware, and some odds and ends), keep as much of your stuff second-hand as possible. Give things new lives and save them from landfill! Gifted, thrifted, rescued, clearance sounds kind of catchy, but there is more! My rules set for getting new stuff is...
Gifted - Hand me downs and gifts, stuff that people give to me.
Thrifted - Second hand shops. Anything from an antique shop, vintage market, op-shop, tip shop, or online second-hand stuff. This is how I get most of my clothes, homeware, and media, as well as some tech.
Rescued - Saved from being thrown away. For me this looks like asking my friends to give me their dying stuff (clothes mostly), going on hard-rubbish-rummages at hard-rubbish seasons, and asking shops if they have any 'unsellables' that they'd be willing to give/sell to me.
Clearance - If I absolutely need or love a product, and I cannot get it in any other way, then I wait until I see it on clearance, since it's probably not going anywhere good if it doesn't get sold.
Local/indie - Sometimes I buy stuff new, I am flawed and evil and such, but where I remember I keep it to local and independent small shops. It costs a little more, but raaaa economic sustainability.
DIY - Making things yourself! You know where it's all sourced, you know how it was made, and you feel a special little attachment to a thing, so you'll want to look after it. On top of that - new hobby :) Now you get to have fun and a thing. I'm gonna make a whole dinner set soon; cups, bowls, plates, etc. I love pottery.

Foster community.

Trade things, borrow things, share knowledge and skills. Nurture your community and the circular economy! Give your used stuff to people you know, or set up free take boxes, or donate them to clubs/educational spaces (pre-schools always love toy donations...). Before you buy something new, see if you can borrow from someone. Trade service for service with people (this one isn't about sustainability per se, but it is good practice!). Set up neighbourhood groups online! All this is mostly enacting the other parts of this section, but they are wonderful to implement, and will let you connect with people.

Personal care & Hygiene

Reusables.

So, you hate spending money! Good news; you'll only have to do it once now! Buying everything you can in a reusable form is probably the most obvious (and probably slowest) change that I'll suggest. Whenever something disposable runs out and it comes time to buy a new box, opt for the most long lasting thing you can reasonably get, then never buy a new razor again. Yeah sure, cutting down on disposables saves money in the long run, but it also hugely reduces waste and (in my case) prompts a sort of mindfulness about where and how you use things.

Waste free swaps.

Swapping from buying plastic or heavily packaged versions of things into buying minimal-waste or waste-free. As well as plastic packaging and all, there's the issue of water in stuff that doesn't need water in it. An insane amount of stuff comes in solid versions, like soap, shampoo, conditioner, and even toothpaste. These solid versions give you more uses by weight, which is why they often seem like they cost more, and reduce unnecessary water use. Shopping at your local crazy-hippie health shop will also be very beneficial for this. Guaranteed to stock at least one beeswax wrap!

Refillables.

An extension of waste-free swaps! Lots of hair salons, and also shops like The Body Shop or those super hippie whole-food places, offer refillable solutions for the times that people can't or won't use solid hair products. Hair salons are a good choice for people that need extra ingredients, like medicated or toning or otherwise special hair products. Hippie-type shops tend to sell lots if they sell anything. Usually this stuff is done by weight or volume, so you can usually use a pre-existing container.

DIY.

Okay so this can be a bit tricky and time consuming, but also very rewarding. Where I can, I try to make things myself rather than buy them. Stuff like beeswax wraps and perfume oils and such. You get to be completely in control and incredibly involved in your stuff, you can find new hobbies and fun, and you can even make people gifts from what you learn. Sure, it may not do much for sustainability on its own, but it lets me make my own choices, and means I don't have to sacrifice my wants for my morals. I can have lavender perfume now! Such fun.

Using raw ingredients.

This is less 'sustainability' and more 'I'm a bit of a hippie', but it applies! Using raw ingredients over weird compounds and mixtures means that there is less machining and processing, meaning less energy and product waste. It also means you're not using things that you don't need to use, therefore not having stuff that you don't need to have or packaging that you don't need to have. Also-also means that there are less bits of plastic and packaging being used. A lot of the stuff in this general umbrella is multi-purpose and really good at what it does.

Food

More whole foods, less packaged foods.

Being vegetarian, there's a weird amount of ultra-processed crap waved in my face at the shops. While I could go on some rant about associated health issues and 'big food', i will keep this rant to sustainability.
The super processed stuff you see in shops (e.g. every sweet, meat replacement, ready-meal-kit) is also super impactful to the environment. All of it involves machinery and water usage, as well as taking up extra space and increasing food mileage.
Food mileage, for the unaware, is the distance a food has to travel to get from fresh produce to your plate. Take a hypothetical capsicum! It makes one trip when you buy it from the farm (farm to your home), and (at least) two when you buy it from a market or grocery shop (farm to shop, shop to home). The trip to the grocery shop costs fuel and associated emissions, as well as power for refrigeration, in transit. If that capsicum is preserved and added to a meal kit, it has to make (at least) one extra trip (possibly overseas!!). This costs more fuel, more refrigeration, and, now that it's being processed, energy and water and such that the machines used in processing need.

Shopping local.

Buying from local farms and shops reduces food mileage. At supermarkets and such, you can't always know where your food comes from, but at smaller shops you can usually ask and make your own decisions from there. I try to buy my shelf ingredients (stuff like flour, sugar, dried lentils/legumes, spices?) from those shops that let you fill your own jars. I can know exactly how far everything has travelled, therefore minimising food miles by picking and mixing my shops. On top of that, they let you fill your own tubs! Gone are the days of silly little paper/plastic bags to decant! Ingredients go straight into their homes as soon as the old stuff runs low.

Gardening.

The ultimate reduction of food mileage, and also insanely customisable to your needs and environmental wants. While it does have a pretty big time and space investment, it is so rewarding and so worth it if you can do it. There are lots of ways to grow things from stuff you already have in the fridge, expect a page on that some day soon.
Gardening is incredibly flexible, letting you grow things that work well for your cooking wants, so long as you work with your climate. You have complete control over what chemicals and processes are used in your food, and you are introducing more plants to the world. So long as you know how to manage your environment (or stick to pots), you are doing a net positive, especially if your plants encourage pollinators or other beneficial organisms :)
In the chemicals thing, if you don't use any, then you know for sure that you're not contributing to any pesticide or herbicide resistance (which is when pests/weeds develop a sort of immunity to chemicals, making them a way bigger problem), and not accidentally harming any beneficial bugs or plants. It also keeps your water ways a l ittle cleaner since there's zero chance of run-off and whatnot.

Foraging.

This one's a bit weird, but if you know your local area and plants, and you know what is and isn't safe, it is not at all a bad choice. (Urban) Foraging is, to put it simply, taking what you find. If you see an edible plant, take a little home. In my area there are some edible weeds (namely fennel) that nobody poisons, so I like to grab some when I walk past and it's in season. Again, very few food miles, whole food, and as long as you only take a reasonable amount, you're not really impacting much in any direction.

Eating in.

Eating at restaurants takes your choice out of your food! Woah food miles again, although you can probably ask the restaurant where they source their ingredients, but also, commercial kitchens make a decent amount of food waste, and, as a fairly small person, so do I with restaurant portions! They are huge. I cannot cope. I have a tendency to order a meal, not finish it, ask for a takeaway box, and then forget about it. Now I have a plastic tub and a half serve of shame. Also in the vein of plastic tubs and shame, in the case of fast food and takeaway food, there is even more waste! No silly cardboard boxes come out of my kitchen! And again, energy cost, processed food, blah blah blah. You've heard it all already.

DIY (again).

This one's for spice mixes, condiments, certain ingredients, and staples. You can make so much stuff in your own house and save yourself tubs, money, and needless purchases. I'll link to a list of my favs later once I have built it, promise... Until then! Making your own condiments and staples means that you have to be more mindful of the things that you like, stopping you from building up jars and jars of shit you never use. It also saves you from the packaging in buying stuff like yogurt and bread and whatnot. I find homemaking super fun, if you can't tell..