I just bought (off fleabay, so we'll see) a pair of the Wald 582 Rear Folding Baskets for my groceries/commuting. My rack pack with foldout panniers (the delta day bag) just wasn't cutting it and I have lots of nice backpacks I can throw in the foldout baskes, use a bungee net to hold in place and take out and work and just fold up the basket. Should work for groceries as well if all goes as hoped. I'd thought about going with some nice waterproof ortliebs but this seemed more practical and cheaper in the short term. Whether it'll work and hold up over time keeping the long term costs down, we'll have to see.