I use Baggies. Sometimes they are hard to find. I get them at WalMart. They come with twist ties, but I just tie a knot. They are easier than the ziploc or fold-over sandwich bags.
If you are ever near a swapmeet or place that sells bags to vendors, you can get a whole case of small bags really cheap. I like the black ones.
Now that I am no longer near a big Flea Market, I use the Baggies.
When I go out picking up poopies, I tell people I am hunting for eggs -- you know like Easter eggs!
