On our retreats, we have prayer partners. They are similar to Secret Santas. Have one of the youth leaders write all the names of the people attending the retreat, and place them in a hat. The attendants then draw a name out of the hat. They are not allowed to show anyone the name, or trade names. (they may ask a leader who the person is if they don’t know.)
They are supposed to write letters to the person whom they chose throughout the weekend. The letters are to be nice things only!! They are also to stay anonymous (they reveal who they had picked at the end of the weekend in a prayer service). We have always made envelopes before we explain prayer partners. Simply take a manilla envelope and supply campers with markers to write their names. They can draw anything else as well. Then, throughout the weekend, they can receive letters anonymously from their prayer partners and letters from friends as well.
I have found that this is one of the best experiences on retreats, as it is something you can take home with you. Whenever I get down, I look at the nice letters people wrote me. =)