Despite disbelif by many, there ARE excercizes you can do away from the piano, not just on vacation, but every day. That is the first thing I had a new young student do before we even sat down at a piano and looked at music or learned C.
Ok, first one: Hold your arm out to your side, bent at the elbow and the palm of your right hand face down. relax your hand and straighten your fingers so that there is still a slight curl to them. Now, take your other hand and start with the index or second finger. The idea is to place the index finger of your left hand on the top of the last joint in the right hand finger, and your left thumb under the tip of the right hand's index, and gently try to pry it "open" (up). Then you have to flex to try to keep the tip, and only the tip of the finger from being pryed open. The rest of your finger and arm should remain straight, only trying to flex the tip. Do this with all the fingers, the thumb is exempt.
You must realize that this must be done carefully, and gently or you could potentially harm yourself. Second, this excercize, and others like it that are done away from the keyboard merely promote technique, and will not help your brain remember your songs when you finally do touch a piano again. However, some time off from piano is a good thing to allow your muscles and ligaments and tendons to relax and heal, but too much time can certainly make you rusty. If you are confused by my instructions, or if you even want more away-from-the-keyboard exercizes, feel free to email me, I hope this helped.
Topic: 3 weeks of vacation without a piano !