Kathmandu, an outdoor retail chain in Australia, offers a neat red back pack that scrunches back into its own pocket to become a hand-sized bundle. I have had two and found them invaluable on all sorts of trips, but particularly for going to the shops after setting up camp, tripping around big cities, and as carry-on luggage on aircraft (clothes only on my last flight). I used them at home for shopping, too. It weighs 200 grams
Outdoor retail chains in North America would offer something similar. I also bought a tote bag in Boulder, Colorado, that compacts into its own pocket to a size just larger than a wallet and that has survived several international and domestic flights also full of clothing and other stuff. It weighs 100 grams. But I can't find it right now to tell you what outdoor shop offers it... something like REI, I think.