Thanks very much to Michele Challis, who posted this idea to the Guiding Mailing List! She learned this activity from Valerie Bell, a White Oaks trainer.
This is an ideal exercise for a weekend camp. Each person makes a party cracker (e.g. the type commonly found at New Year's Eve celebrations that require two people to pull it apart and it snaps). Make the cracker using an empty toilet paper roll, some tissue paper and ribbon for the ends. Leave one end open and write each person's name on the outside. Then all weekend, whenever possible, everyone drops a kind thought or word into someone else's cracker. At the end of the camp, the crackers are sealed up and taken home. The idea is that when you really need a boost or a smile, you can open up your cracker and read all the wonderful thoughts about yourself written by other people.
This could be altered for a regular meeting by allowing everyone time to write nice thoughts etc. for the crackers, seal them, then open them the next week.
The only downside of this is that if a girl doesn't have anything nice to say about someone, you'd hope that she wouldn't write anything bad. Perhaps screening might be helpful if that was an issue in your unit.