I've permanently attached (it's riveted) a bag to a plate that simply replaces the standard seat. As I never take a pillion, it stays on all the time, but can be easily swapped for the proper seat if needs be. Holds the chain (Pragmasis 1.5x13mm... if I carry it), a D Lock (which I always do), Compressor, spare gloves (sometimes), bottle of water etc. etc.... works very well.