Handing out ice cream is exactly what they did on the "Lange Nacht der Wissenschaften" (Long Night of Sciences) in Berlin. They froze it right in front of their audience, wearing white lab coats. Handing it out made them quite popular.
A small science show with all that colorful fluids becoming another fluids, Mentos in coke, things with water (
http://www.cracked.com/article_17276_5-scientific-ways-make-water-do-magic.html) would be nice, but I don't know where you would do something like this and what target audience would be interesting. But you would do it for the video, as long the people watching are entertained.
Needs training and material, competing with youtube and TV is hard.
Oh, do it in front of a cinema, when you've seen Star Trek enough. Plenty of geeks, waiting for the movie. And you could also promote TSF, that would be quite cool. (At least in my mind...)