Depends on which band.... Either I haul my own setup in my pickup truck (sometimes plus subs, covered in garbage bags if rainy), or I carpool with a guitarist who has a minivan (with seriously tinted windows!).
If I'm not bringing lights, I can put my amp, basses, tote of cords, and emergency briefcase in the cab of my truck (amp gets front seat, basses behind seat). Don't think I'd want to haul a trailer, too hard to drive (did it once with a load of animals...whew!) and too tempting to leave everything in it. When the outside temp hits 90+ it's too much for equipment in a trailer! Van or truck (if you had a topper, even better....pita to have to go straight home).