Remember a couple basic rules:
1. Turkeys loose 50 % starting weight, 12 lb bird yields 6 lbs.
Hams loose 30% starting weight, 6 lb ham yields 4 lbs 3 oz.
Oven roast/ pot roast loose 25 % starting weight, 4 lb roast yields 3 lbs.
2. The more meat selections you have people usually take less of each.
One meat                                  2 meats                                         3 meats
Turkey 12 lbs                        24 servings                                  32 servings
12 servings                            4 oz portion                                   3 oz portion
8 oz portions                                           

Baked ham 6 lbs                    16 servings                                  21 servings
10 servings                             4 oz portion                                  3 oz portion
6 oz portions

Roast beef 4 lbs                        12 servings                                 16 servings
8 servings                                 4 oz portion                                  3 oz portion
6 oz portions

Note: Uncle Joe may eat more that this chart says, but Aunt Lulu may eat less.