The youth ministry blog "Confessions of a Human Being" offers up a series of posts with some excellent tips for leading a retreat with your youth. Here's one I particularly like:
Ban Personal Electronics - The two major factors of most every retreat are building community and getting away from the hustle and bustle of life. Anything that requires headphones will automatically cut a person off from the group, and cell phones, PDA’s, etc. being present are not getting people away from life’s bustle. Do not allow students to bring anything that falls under this category, or you will be fighting an uphill battle the entire trip.
Read more here.