Prints, Stickers and Keychains! Oh my!

One of my goals in life is to sell my art at a convention! I've tried messing around with things such as making them into little stickers and such. I've also tried printing my own prints which...didn't go too well to say the least. Have you guys ever turned your art into little things like these?

I've mainly tried stickers. They're easiest because I can just print them out on some sticky paper and cut them out in the shape I want. The print disaster was because it wasn't the right type of paper so it got smudged everywhere ;;