I was talking with
hurkon the other day, and we came up with the idea of an ikebana (Japanese flower arranging) gathering some Saturday soon (while the Farmers' Market still has good flowers). We'd go to the market, get one to two bouquets per two to three people, then go somewhere with a good bit of table space (potentially somewhere outside, if not too windy) and do some ikebana.
Each person would just have to bring a container or two they think would be fun to arrange flowers in. For the style of ikebana we would be doing, the containers should generally be at least somewhat wide (at very least having an opening, say, three inches in diameter), and it should be easy to reach into the bottom of them, and they should be capable of holding something like half an inch of water at minimum. Beyond that, just about anything goes. Bringing scissors and shears good for small plants would be useful, but not necessary for everyone to do, and I'd make sure there were enough kenzan (pin frogs, the things the flowers will stick in).
You can see random examples of ikebana I've done on my flickr:
http://www.flickr.com/photos/99071083@N00/tags/ikebana/ Post if you're interested, with what Saturdays work for you (and any time restrictions you have on those days; the basic flower shopping and ikebana portion would probably take about two hours, more if people are having fun).