Everyone has some of these lying around the house not being used. There are lots of uses for these. It's great for watercoloring if you are a kid or an adult.
Another good idea is when you have to put furniture together or work on a project that requires lots of small screws, studs, tacks, etc. You can separate how much you need using an ice cube tray. It's easier to quickly grab it when you need it and you don't have two hands to fumble with the packaging. Arrrgh, that difficult to open plastic pouches are so difficult to open without scissors.
For moms, you can use them to separate little hair clippys or ties. They are shallow enough to be easily stored in a bathroom drawer. I like this idea because my daughter wears two pony tails and I don't have to dig to look for a matching set. It's all right there. So it's a time saver for me in the morning when she gets ready for school.