Learn to cook & meal-prep. Invest time into your health and fitness. Self-host as many techy services as you can (bonus points for Arr stack - streaming services are expensive). Try to “BIFL” where possible - Terry Pratchett said it best:

The reason that the rich were so rich, Vimes reasoned, was because they managed to spend less money. Take boots, for example. … A really good pair of leather boots cost fifty dollars. But an affordable pair of boots, which were sort of OK for a season or two and then leaked like hell when the cardboard gave out, cost about ten dollars. … But the thing was that good boots lasted for years and years. A man who could afford fifty dollars had a pair of boots that’d still be keeping his feet dry in ten years’ time, while a poor man who could only afford cheap boots would have spent a hundred dollars on boots in the same time and would still have wet feet.