It depends on when we are there. At Christmas time I always tip 2 per bag, 3 for oversized/over weight, and an extra 5 for all of the little things (think cosmetic bag that wouldn't fit in suitcase, carton of soda, DD's stuffed animals)
One year the bell hop walked out with 50.
During regular season I tip 2 per bag regardless and I carry my own "little things" or leave them in the car to get later.