I can't abide with anything on me while riding (well aside from clothing of course) so I use panniers. For non-work rides, sometimes I use a trunk bag. And I have a basket for my folding bike. The downside of panniers is carrying them off the bike. I have old Nashbar panniers and they are not comfortable to carry around if I need to walk around for a bit. They just have one small handle strap.

They are old and ragged so I'm actually considering leaving them on the bike. Maybe even zip tie to the rack lest someone is interested in old raggedy panniers. That way I can plop my backpack and regular bags/purses in them. If they are ever stolen or give up the ghost, I would consider the Wald folding baskets. My concerns are rattling and weight of the baskets.