I would suggest a wet tee shirt contest but no one ever takes that serious so how about two ideas I just now came up with: One is you have 4 containers of cut flowers and you choose up 4 teams to make a theme arrangement and award a prize for the best one.
Two is you have 4 piles of assorted junk and you organize 4 teams to build some sort of yard art from their pile (supply wire, paint, glue gun, etc. ) and have a judging for the best one. You might even have gag gifts for the winner and the runner ups. You might come up with some sort of plant game show where the emcee gives the botanical name and the contestant gives the common name. Not knowing what type programs you have had in the past this is the best I can come up with on the spur of the moment. Lastly, you could always hire me as a speaker and I will have them rolling in the aisles laughing.

Daisy, What have you done for your "hort day's" in the past? Not every group has "hort day's". We have a speaker series at the main office in the Fall. We've had talks on bulb forcing, composting, putting your garden to bed for the Winter, a hands-on hypertufa class, designing your garden, propagation, care of roses, container gardening, weed and insect identification. A county near us puts on a one day seminar with classes on hypertufa troughs, flower arranging, propagation, photographing your garden, tree identification, what's new in annuals and perennials for the upcoming year. It was usually a brown bag so we didn't have to worry about food for everyone. Billie

Eddy you sound great...how much do you charge???? Billie ann, we have had wonderful speakers on most that you mentioned..but the hyptufa would be a nice idea ...thanks much...