Become a better musician while on vacation (without practicing!)
Unwind. For some, this is exactly what you are looking for on vacation, to take a break from the daily grind. But for singers and musicians, unwinding may end up winding you up. Stopping your practice sessions can slow down progress. Worse, some things that have taken time to learn can be easily forgotten, some automatisms fade... For example, a guitarist working on chord progression certainly cannot afford to put everything on "stand-by" for several weeks.
It's difficult for a drummer to find space for such a voluminous instrument in the trunk of the family sedan, but when it's time to close the trunk and hit the road, it's certainly not impossible to continue learning music.
In the absence of intensive practice, theory, listening, and observation can be good ways to stay in-tune and in-shape.