I whipped these bags up last night using some bits of fabric left over from other projects. I used a free pattern from Boogaboo Babies (click on the item to download the free pattern). ETA: this pattern is no longer free. Drawstring bags aren't that hard to figure out though, especially if you don't want a lined one.
The bags were easy to make. The one of the left was made from 10"x10" squares, and the one on the right from 8"x8". The first is too large, but the second is an awkward shape. Also, the left one is lined. I like the interfacing on the bottom to give it more support, but I think the lining is superfluous and make for an unnecessarily bulky bag. These bags are to replace Ziploc bags as snack holders, and also allow Maggie to get her own snacks. We don't have a snack tray on our stroller, so we'll use them on walks.