Ditto. I almost always carry a hobo bag, made of strong but lightweight fabric -- about like double layers of strong muslin sheets -- that rolls up small but unfurls to large capacity. Perfect for carrying a few groceries, or bread and bags of chips after the panniers are filled. At the moment I've removed the racks from one bike I plan to ride tonight, so I'll roll up the hobo bag and stuff it in a jersey pocket or under the saddle.