For a mixed group like a wedding, I go 1/2 pound per person, some will not eat, some will just pick at it and some will eat like they are starving, so it evens out. For the men's/ boys group at Church I go 3/4 pound and still have to remind everybody to be gracious till everyone's had some. For really large groups (500 plus), I will serve the meat's to keep from running out and put out smaller serving spoons for the sides. 1/3 cup Vs. 1/2 cup, etc. and let them serve themselves for efficiency reasons. Bread is another area to watch, everybody usually grabs extra, especially rolls, so watch how people are taking and adjust as necessary. I love cooking for big crowds and have never ran out yet, but you have to be diligent.