I spend a lot of my time doing freelance software development, and lately enjoy learning about RF electronics and signal processing.
Gardening has been part of my life for a long time, but my favorite plants are still those useful perennials that fight for themselves: culinary herbs, fruit-bearing thickets, etc. I like "completing the circle" by eating the snails back, feeding scraps to our chickens, getting most of our fertilizer from beneath the rabbit hutch — something of a "permaculture outsider".
Also getting into aquaponics with a greenhouse a few years ago helped me learn more about energy and nutrients and bacteria (and aphids…). I like to understand the sciences, and then fly by the seat of my pants.