A chance to learn how a green screen works and the sorts of effects you can produce with it.
Green Background (this could be a proper green screen or some uniformly coloured green paper), Video camera (or a normal camera that also takes videos), Tripod, P.C. with suitable green screen software (a simple search on google will find you some appropriate software) and a suitable image or piece of video to overlay your green screen footage onto. You might like to ask your Scouts to come in fancy dress or spend some time earlier in the night making items.
Set up the green background.
Try and make sure that it is evenly lit.
Have your actors perform infront of the green screen.
Load the footage onto your computer.
Use the appropriate software to overlay your footage over your choosen video. (I'm personally using t@b)