L.R.
I would really recommend renting a hospital grade pump for your vacation. That way you can get the most efficient pumping possible while you are away from your baby. Also, do some deep massage of your breast toward your nipple while pumping to make sure you are emptying the ducts near your chest wall. That should lessen the chance of mastitis by maximizing your breast emptying while you are pumping. Also, try to do something relaxing while pumping, like looking at a picture of the baby, or reading a book, so you aren't just obsessing about the bottles getting fuller. And last but not least, drink plenty of water so you don't get dehydrated and have the work against you, and pump on a schedule at least as often as the baby nurses at home. Still, even while doing all that you might have a little bit of a production dip while you are away. Try to plan for a day or two after you get home to spend lots of time in close contact with the baby and nursing very frequently to get your supply back up.
If you do notice that you are getting blocked ducts, hard spots or discomfort while you are away start immediately taking antinflamatories like ibuprofen for the pain, apply heat for ten minutes before pumping, and massage out the lumps while pumping to release the milk. Also, if you don't feel like you are fully empty after pumping, try to pump for five minutes after you stop seeing milk to try and get another let down. Hopefully those things can stave off a case of mastitis before it gets bad.
Get plenty of rest, have fun, and good luck. :)