An idea RedBike: if you always go to the same cafe, then can you not just leave a lock permanently locked up outside the cafe? Or if there's say 2 or 3 regular cafes you usually stop at, then just get a few locks and leave one locked up outside each one. Then you don't need to carry it with you, but you've got your security whenever you need it.
If your cycle club all stop and park their bikes there, then depending on how amenable they are to it, and what sort of provisions for locking up there are outside the cafe, then you could club together and get a big thick chain for all your bikes?