Ah, I didn't think of other ways of using the s-frame. Nice. I do have Brompton's folding basket, but I don't want to put anything fragile and expensive in it for fear of it just popping out on a rough bump. I've noticed the small wheels are a lot less forgiving than those on my other bike. Also, things that need to stay dry really shouldn't go in that basket.

The Brompton rack sack might be the best solution since Brompton designed it specifically to work with their bike and it is the only one. I'd just like a few options like they have for the front.