Rent them from Redbox. They charge $1 a night, and you can rent from any redbox and return to a different one, so it's great if you are traveling. You can also buy used movies from the Redbox for $5 or $7 (though it looks to me like not all redboxes allow this option)
If you have Netflix, just put them at the top of your queue so that you get them prior to your trip, then keep them during your trip.
Finally, ask family and friends if they will let you borrow theirs, or borrow from your library.