This is the table developed by Reed Kennedy detailing how much underwear to pack for a trip depending on the length of that trip, and how many times you'll have to do laundry to keep those underwear clean (provided you don't wear the same pair two days in a row because you got drunk and slept in them and never changed before leaving to go drink your hangover away the next morning). The numbers located in the inside boxes are the number of times you'll have to do laundry (with the gold numbers being ideal). Want to pack as little underwear as possible? Don't bring any. After all, you're going on VACATION. If a person can't NOT wear underwear on vacation, are they ever truly free? That was rhetorical. When I go on vacation I only bring the underwear I wear for the flight, then when I get to my hotel I immediately flush them down the toilet, clog the toilet, then go demand a room upgrade. It's only worked out 1 for 4 so far, but that's still successful enough for me to try again next time.
Thanks to Bryan, who doesn't pack underwear for vacations either, because, just like sunscreen, they probably sell underwear where you're going.