Often times when I am on vacation during the summer or have started a new piece but want to keep the old piece in my fingers, trouble ensues. I believe that family always comes first and if you are on a vacation with your family doing something special, you need that time to take a break and enjoy the company. The only trouble with that is that when you get home, practicing is even more of a drag.
Even though this may be a hassle, it is worth is to bring your instrument with you on your vacation so that it will be in the back of your mind. Even if you can’t play or bring the instrument, listen to your reputoire everyday. Bring the scores and continue to study the scores if you have your instrument or not. Everyday remind yourself of the hard parts of your concerto and how you have learned to play them well. In short, remember the certain tricks you (probably) have learened that help you play the hard parts better. Visualize yourself playing the piece for just 5-10 minutes everyday.
If you have your instrument, just take it out for maybe 10 minutes everyday and just go over one or two common problem areas with slow practice, a drone, or a metronome (or any practice method that you think would be benefical) just to keep the hard parts still in your fingers. If you have time, jsut play the whole piece through at the end of the day to make sure it stays in your memory so that you will stay ready to perform it for when you return home.