As others have said here, I tend to spend a lot on computers, specifically a lot on computer hardware personally. I work in tech, and when I get home, I like to tinker and see what fun stuff I can do with them. I find it a very mindful, grounding, and fulfilling activity. I'm also a big fan of free and open-source software (and I'm also on lemmy, surprise surprise) so a lot of what I do is rigging up FOSS solutions for friends and family like a Jellyfin media server or a retropi. I'm very lucky that I'm currently in a position where I can afford small hardware expenditures like that and give them away to people who can use them. It makes me feel good, plus it (hopefully) popularises free software in my community!

As inasaba has said, Stoic philosophy is very helpful for simple living, but a book from a different school of thought that I really found quite a bit of value in is How to Do Nothing by Jenny Odell. It discusses a variety of ways to resist the attention economy of social media while also not becoming a hermit, by building small, local, and intentional communities, and setting aside part of your day to just mindfully doing something that brings you joy (The titular 'doing nothing') Plus, it's popular enough that there are usually a few copies at your local library. If that's not simple living, I don't know what is!