Ditch the junk you don’t need to carry around in your vehicle.
The lighter the load, the less weight you are driving around with, which means your car uses less gas while moving.
This is likely not a huge factor for most people, but for those of you carrying excessive items in your trunk, hatchback or SUV (perhaps some bags of soil for your spring garden that you keep meaning to put in the garage but forget) we’re talking to you!