Left hand, you can take along the sheet music you're currently working on, and practice the fingering for it. You can't practice intonation (i.e. getting the notes right) very well, but you can at least practice which finger on which string in approximately which location.  You'll have to refine it once you get back to your violin, but you should have the music fairly well memorized after three weeks of practice like that.  (You might could cut out a fingerboard-shaped piece of cardboard - don't know how well that would work by itself, though.)

For the right hand, take anything long an skinny (a pencil or pen will do) and practice your bow stroke, paying lots of attention to the movement of your wrist (down at the frog, smoothly moving up towards the (imaginary) tip), making sure your upper arm is not moving forward and back. And imagine playing different strings, so that you move your upper arm up and down - you might be good at not moving it forward and back on one string, but unconsciously do it on another.

Then, when you get home, grab the violin and find out how much of that transfers over to the real instrument. Expect it to be rocky at first - you've been playing an imaginary instrument, and fantasy always goes better than reality.  But after a few hours of working with it, I think you'll find that all that practice you put in on vacation will be paying off handsomely. You'll have done a lot of good work, you'll just have to make the adjustments to doing the same things with the real-life instrument.

Hope that helped.