For game play purposes, one person can bring one box of field supplies to a field or town. It is set that way for the purposes of game play.
Now when you are talking about vehicle supplies or troops, that's a little different. A jeep is much faster than an M3 or LVT, but it doesn't carry as many troops or vehicle supplies. So there is that. But when it comes to field supplies, HTC has determined that it would throw the game play too far out of balance to have the C47 carry more troops or field supplies.
