Good point on the writing everything down for future reference.  I have a recipe box with all those sorts of things:  the boys' graduation parties, the sandwich stands that our 4-H club ran for a local auctioneer, the bridal showers, baby showers, etc that we've done over the years.  It's paid off.  I'd rather eat leftover "whatever" for 2 weeks straight than run out of something at a gathering.   Once you have a clue of how much it takes to feed a certain sized group, it's a lot easier to plan.