Between my husband and me, we usually take:
one suitcase each
one large duffel bag that we share (only about half full)
one garment bag that we share
one backpack each (this is what we use for carry-on, works great for excursions)
packing hint: if you and spouse are each taking a suitcase, pack half of your clothes in each, so that in case one gets lost somewhere, you still have clothes.