Here is a general guide - based on average portions.
Turkey - allow approximately 1.5 lbs (675 g per person). For turkeys under 14 lb allow approximately 2 lb (900 g) per portion as the bone to meat ratio is higher for smaller birds.
Goose - allow 2 lbs (900 g) per portion. The biggest geese are only about 11-12 lbs (approx 5.5 kg) so if you need to feed more than 6 people you will need 2 geese.
Chicken (whole, on the bone) - allow 1 lb (450 g) per portion.
Duck - allow 1 lb (450 g) portion.
Pheasant - 1 pheasant feeds 2 people.
Guinea Fowl - 1 guinea fowl feeds 4 people.
Ham, raw. Order 8 oz (225 g) per portion. This will give you 4 oz (110 g) of cooked ham per portion. Ham loses approximately 1/3 to 1/2 its weight in the boiling process, so if you need 2 kg of cooked meat, you should order 4 kg of raw ham.
Meat on the bone (e.g. Rib Roast) - allow 1 lb (450 g) per portion.
Meat, boned (e.g. Rump roast/Topside Roast/Boned Pork Loin) - allow 8 ounces (225 g) per portion.
Meat boned for casserole (e.g. venison casserole pieces) allow 4 oz (110 g) for a casserole with equal vegetable ingredients e.g. mushrooms, onions, carrots. If the casserole meat is just poached in wine, allow 8 oz (225 g) per portion.