and bought a bike.
Trying to talk Havocdad into building a solar oven. Telling him I could make cookies in summer when I normally do not bake because it heats up the house. (gotta know the right hook and bait to use when ya go to reel something in

)
Planted more clover as it is dense and slows weeds, it shades the ground and cuts moisture loss which also prevents grasshoppers from using that ground to lay/hatch eggs so I don't have to use chemicals to kill those plant eating pests, the blossoms are good for my local bees, it fixes nitrogen in the soil and cuts the need for fertilizers/ helps my garden grow
Put more sun shields over windows in summer. Insulation in walls too, for summer and winter comfort without as much fuel use.
A chillow for my nighttime comfort with less use of ventilating devices.
oh, you said ONE. Sorry. My bad

It is so easy to find ways to do better. Make it a game for the kids.