It's been ages since I have been to a hens night... but one where I helped organise games was for my Aunt and we had her do a treasure hunt.
We all wrote a list of things she had to do, like get a condom of a guy, get a guy to do a strip tease for her, get someone's boxer shorts, get a kiss on the cheek from a guy that we chose etc.
In the end she had everything crossed off the list and it was a hoot! She loved her night and we all had the best time helping her.