If you are willing to buy zip-lock bags, they are available in heavier thicknesses. I just picked up an order from Fastenal that was picked and packed in very heavy zip lock bags, and picked a few extra out of their waste can at the counter - guy thought I was nuts! Uline sells zip lock up to 8 mil, and they are only 10 to 20 cents apiece, but you have to buy 1,000! I am sure if you root around the Internet you can find other options that are a bit more affordable. Or maybe buy 1,000 and give them out to your A.S. friends in batches of 20 or so!
Philbert
"2 Mil. is the standard industry thickness. = 50.8 Microns = .0508 Millimeters = 2/1000 inch. The standard household Ziploc® Brand sandwich bag is 1.5 Mil. The heavier freezer bags sold in stores are about 3 Mil."
EDIT: Fastenal sells 4 mil zip lock bags pretty reasonably in quantities of 100. Search for "4 mil Clear LDPE Reclosable Bags". More on Amazon and eBay.