Whatever I can pack in there. No back seat, just a shelf to pile crap on and storage underneath. One thing learned on Power Tour is you always need something and there is never enough room in your trunk for all the crap that seems to show up.
In the storage compartment built in my back seat is 700 watts of XM. The cover is hinged and covered in carpet. Plenty of room to throw a few duffle bags. No room in the trunk because of the battery and fuel cell.