I use the Wald folding baskets on the rear of my frankenbike. I can get usually get 2-3 of those plastic grocery bags in there, if necessary with one bag extending out the top and a bungie strapped across from one basket to the other. I also zip-tied an old wire letter basket to the top of my front rack, which is good for another bag if I need it, again with a bungie. The folding baskets are also good as a wider platform than just the rack if I need to carry something large.