White Glue (Elmer's works fine)
Your design(s) printed out on paper*
A wide brush
Tupperware container OR jar (optional)
Packaging tape OR Clear Contact Paper (optional)**
Little spray bottle (Recommended)
Scissors OR X-acto Blade
*Regular printer paper works the best I've found. I printed some on matte paper and the adhesive didn't absorb into the paper, making for a weaker sticker.
** Utrecht's art supply carries this in about 36" rolls. It's also great for making very crisp stencils. The only bad thing about this is it rips easier than the tape. It's also a tad expensive, last I remember.
Design Tips: Try to fit as many stickers as you can on one sheet. With rectangular or square stickers this shouldn't be a problem. But with stickers with a more dynamic shape I like to leave about an 1/8" border around the edge of the ink.
A lot of people have been asking me if it's okay to use a different kind of vinegar over the years. I'm going to say no, and read the comments. White Vinegar is stupid cheap and the purest, so it won't discolor your sticker stock.