I use the bags intended for freezing breast milk to freeze wort for starters. They're about eight ounces and I can usually get four of them filled from just letting the grain bags drain into a bowl.
For yeast, though, I've always just poured the yeast cake into Rubbermaid 1-liter plastic storage bottles. Unless you have a more precise procedure, I would think pouring into a two ounce container could get messy.
All that said, there's no reason you couldn't use them to store yeast if you want to. I agree that they would be a good size for growing in a starter.