How serious is the group of people? This is the number one deciding factor on what to get.
Gag gifts are always good when the swap is purely for entertainment.
For example,
last time I was in one with a bunch of friends I gave a 12 inch dark brown sausage in clear packaging. Got some laughs. The receiver, who was a dude, was actually stoked after he got over the innuendo part cuz he really liked sausages.