Getting rid of car centric infrastructure and city design, and make cities walkable and massively overhaul public transportation, for example.
Some will say that doesn't apply to them, but most of the worlds population live in urban centers of some sort. Having a car is a totally unnecessary expense when you live in a well designed city with good public transportation, but for most Americans you need a car because our cities are designed that way on purpose - to force you to buy a car. For most people, especially lower and middle class folks, their lives could be massively improved with this one small change, because it would drive other changes. If you're out walking or riding a bicycle in your neighborhood instead of taking a car because there's high quality paths on which to do so, you'll meet more of your local community, experiences the positive health effects of being outside more often and so on.