Ideas for a surprise 40th Birthday Party flier?

I need to make up a flier for my dad's 40th birthday party. I need everything from wording to colors. It's going to be a barbeque/cook-out type thing and I'm not sure how to incorporate that idea because I personally think that having pictures of hamburgers, hot dogs, and a grill on a birthday invitation is quite corny. I don't think I have any pictures of him as a baby/child, so that idea is out of the way. I'm not sure what else to do, any suggestions?