I tip $2 now for the crew van. More on a family trip.

For the cheap tools who don't tip... no, you're not paying them extra just to do their job, their compensation is based on the assumption that they'll get tips (if they don't suck).

That said, no tip if they're late or don't load the bags... that's part of the job, so if only do part of the job they only get part of the pay. Doesn't bother me, I'm happy to load my own bags and keep the $2.