They're cheap - usually you can get them in a pack of 100 for around $4-7 - and you can find them in a wide variety of sizes. They offer some measure of protection and waterproofing. And they do the job of organizing quite well. You can sharpie 'em or label 'em if needed, but I usually don't bother.
You can find these baggies at craft stores like Michael's, Joanne's and others. Or they can be found online; Amazon has a wide selection of various sizes