I'm really interested in learning; the topic sometimes doesn't matter, but recently it has centered around programming and finance... some other more random ways I stimulate by brain is by watching How It's Made, or clicking through Wikipedia.
Sometimes I have to remind myself to live in the present; I'm the type to criticize the past and worry about the future. I find that new experiences are the best way to keep me focused on what is right in front of me.
I like browsing reddit, and will inevitably relate an experience to you in the form of a meme, or cat picture... maybe a duck, you never know.
One of my favorite things to do is travel. When I go away I usually mix it up, back-packing, staying in hostels, a hotel here and there, and a lot of walking and exploring. I'm not a big picture taker when I'm by myself; maybe in the future when my memory is going I will regret that decision, but it seems to me like, here I am, there I was, doesn't really matter all that much - so long as you can remember the stories to retell.
Some other random things... I like to play guitar, surf, snowboard, shoot sporting clays, play tennis, kickball, and volleyball, buy new gadgets, test drive new cars, and I'm seriously considering taking up hang-gliding (but haven't quite convinced myself to make the first step).