Last time I organised a hen night I made a big poster board the she had to wer (big board on front of her on one on her back. On the front was a task list which she had to accomplish. She was marrying an architect, so one of the tasks was that she had to find an architect and kiss him. Another thing was that she had to procure a condom, which she managed from the bartender within 10 minutes at the first bar... hmmm.
Also, give the bride-to-be a nice decorated jar to carry around and get guys to donate to it. The she has to buy drinks with it and drink them herself. So you get the locals to fund her drinks basically. This only costs you the price of the jar/cup.