Make things even if it costs more than buying. This requires you to have access to a lot of tools. Especially in the kitchen.
If you hear an advertisement for something that is offering a discount larger than the amount you would actually pay for the item then never buy it from them.
Pay more for something that will last you the rest of your life.
Look for functional items at antique shops instead of buying a nearly identical item new.
Never buy physical media new unless it’s literally your favorite band.
Learn to knit, sew. Even if you’re buying yarn or fabric from a big corporation your handmade good will surpass fast fashion in quality and life span.
You don’t need any merchandising from your favorite movie or comic book. Lego doesn’t count because you can build other stuff.
Pawn shops and thrift stores are your friend. I guess this is a footnote to my first point.
Go through your library’s website with a fine tooth comb to see what services and goods they offer. This conclude free streaming stuff or seed packets that are picked for your area or any number of other things other than books. And of course books.