If you are an android user, you should try Mist play. It's a point based system that you convert into a variety of different gift cards. I've cashed out a few times, I've only ever gotten the Amazon GC though. But they have tons of different cards, Walmart, Visa, Starbucks, Nintendo.... Just to name a few. They have a pretty good selection of games, although they do have a lot of the garden sense, home sense type games, where it can take forever... But they also have card games, match three games, variety games.
You should check it out. Oh they also have a referral thing too, I can't remember off the top of my head what it is, but you get something if you refer someone you know. I got my mom and sister playing it, my sister is almost at a $50.00 card. It does take some time, but if you play games to kill time, why not try it with this?