Interesting - I usually put my foot in a boot, and my bag in the trunk, but to each his own
The Trunk is a large wooden chest, used to carry possessions on expeditions and long journeys. It was usually stored in the boot room of large houses which was near the servant's entrance and also where the dirty boots and shoes were kept before they could be cleaned. Therefore, possessions in trunks were often placed into the "boot" before being carried out to the coach: instructions to the house staff being what to put into the boot! I would assume that American coaches did not have a separate boot, but the trunk was strapped onto the top or back of the coach, leading to where possessions were placed. (American houses probably didn't have a boot room either).