Another vote for the Topeak. Although I sometimes use the Topeak top bag, most of the time a pair of Ortlieb panniers do the trick. For big shopping trips, I add the Topeak top bag, and a pair of Thule front panniers (no mount points on my bike up front, so I have a Thule up front). The special topeak connector works well; but I like to pack more in the panniers than would easily fit with the topeak (so I went with the top bag only, no stealth panniers). Arkel's connector is better than Ortlieb (and I've got a lovely older Arkel backpack pannier). But I bought nearly all my panniers used, and hardly anyone sells their Arkels ... Orlieb is next best, followed by Thule. My Timbuk2's are lovely bags, but the connectors keep breaking.