Anyone have a preferred type of sissy bar/pax seat mounted travel bag?

I'm looking for something to hold a couple days worth of stuff for runs to the camper at the beach.  I have a pair of small saddle bags that don't hold much but are good for everyday riding around.  I want to be able to pack road repair items, cover, rain gear and (minimal) clothes/travel items.

Thanks in advance,

Miles

I've just used a cheap duffel across the back seat. I thought about a daypack or other nice bag but then you have to be concerned about some creap swiping it when you go the the john, restaurant, store, etc. I just put easy, cheap stuff to replace in it (clothes) and keep more valuables in the saddlebags. My camera and sunglasses I carry in a pocket.