Painless economy options

Im replying to BenBlood, as well as commenting on the hype of useless gadgets we are now seeing advertised again.

That pretty much sums it up.  As my college physics professor said, there is no such thing as a free lunch.  That hydrogen thing will increase mileage, but only because it will lighten your wallet.

Change the thermostat if it’s over 5 years old.
Make sure the brakes aren’t dragging.
Over-inflate the tires a couple of pounds.
Check the wheel alignment.