Always pack an overnight bag for long car trips, even if you're not planning on stopping for the night. That way, when you hit a snow storm in Watertown (there's always a snow storm in Watertown), you can get a hotel room and just grab that one bag, without having to dig through all your stuff to find clean underwear.
Or, if you're stubborn like me and you just keep driving and get home at 4:00 in the morning, you don't have to unpack the whole car - you can just bring your overnight bag into the house, and unpack the rest the next day. Or the next day after that. Or, well, eventually, anyhow.