If you are speaking of vacation in the generic term of time off of work...then I am a big fan of sleeping. Also, eating. And extra time at the gym. Maybe some travel.
If you are speaking of vacation in the sense of traveling elsewhere for a period of time, then the answer is TO NOM THINGS. Seriously, for me, if I'm visiting someplace new, I want to experience local food. When I visited San Diego and Tacoma, I made sure to eat at a quality seafood joint that was right on the water. In Brazil, I made sure to try as much traditional fare as possible. Food is a universal cultural experience, so when I travel, nomming becomes a high priority.