I'm getting really good at growing lettuce. Nice simple activity, with a simple reward. I was trying to do it outdoors, but rats came and ate it all. So now it's indoors under lights. It's on a timer, and the lights are on during the time we get lower electricity rates. All I need to do is remember to water it every two or three days. My wife enjoys the heat at night the lights provide.
It costs nothing to run because we have an excess credit with the power company from our solar. It's about half the power her space heater would use, and still keeps the bedroom warm enough.