My DC's school had a "dress up as a book character and then give a donation to comic relief" day. Obv I'm fine with the do something for fun for comic relief idea, but could have done without trying to dress the kids as book characters.
Lots of the parents were struggling to put an outfit together with clothes from home and lots of people will have spent more on the outfit than they did on the donation. A better idea would have been a non uniform or dress in whatever fancy dress you've got at home already and give what you would have spent to the charity instead. Although I am biased as rubbish at creative crafty stuffy...