Side hobbies used to include penning comics and playing guitar. Due to the extremely repetitive nature of my job though that's come to an end. Anything that requires grasping something like a nib holder or finger intensive activities are out. I like reading comics, fantasy books. Listening to music.
Side collections include books. My wife and I both have a love for fantasy books so we have quite a few and are usually picking up ones where ever we can. Music cd's I love heavy metal music and always nab cds when I can. I also have a soft spot for video game soundtracks and have quite a few of those too.
Trading card games. Mainly Magic: The Gathering. I buy most of the side products that come out. Fat packs, gift boxes, Commander decks. I have all the Archenemy, Planechase decks, Duel Decks too. Other games include Yu-Gi-Oh, Dragon Ball Z TCG, Yu Yu Hakusho TCG, Pokemon, Gundam M.S. War. Yeah I'm a sucker for TCG's
Anime DVDs. Something I was massively into as a teen. I introduced my wife to it and now she's way into it, more so than I am. So we have an extensive library of that too.