Karen, as you plant your trade seeds, save the ZipLocs! You can always re-use them for future trades.
If you want to be tidy, wipe them out with a bit of tissue or toilet paper. Remove dust and all seeds. Magic Marker wipes RIGHT off (use a little isopropyl alcohol to get every trace off).
If you want to be incredibly fussy, rinse them out with some dilute real-bleach chlorine-Clorox (not oxygen Clorox) and then try to get them totally dry again. I wouldn't make the Clorox any stronger than 1:10 or 1:20. Maybe one Tablespoon per cup of water.
I get my 2x3" Ziplocs from Wal-Mart. $1 for 100.
