I'm catering my own event for 100 people and need to know how much of each meat and side dish I will need. It will be buffet style and there will be a fair mix of men, women, and children. I will be serving pulled pork, grilled chicken, mac and cheese, baked beans, potato salad, corn on the cob, coleslaw, raw mixed veggies, and dinner rolls. I will be buying the meat pre-cooked so I just need to know the prepared amount needed.
I worked in an Italian place that occasionally did banquets. This is how we anticipated an adult serving:
- Mains (meat / pasta with sauce / fish) 160 grams (or 100 grams of protein per adult, plus 60-ish grams of sauce, garnish, etc - this allows for a bit of extra)
- Sides are 1/3 * 2 of mains, since people generally have more than one side. Roughly 2 servings at 50 grams each, for a total of 100 grams.
- Bread you can do per person at just 1.5 * headcount, add more bread if you have more kids because kids tend to go for the bread.
I would strongly encourage you to drop one side dish, and suggest dropping the raw mixed veggies. You've got cole slaw there and corn, that's more than enough. Because at the number of items you have with absolutely no data on what tends to move the most, you're going to end up with a ton of extra food and likely fall short on what people wanted the most.
For the rest of this answer, I'm going to assume the mixed veggies are going away, because it really does simplify this a bit. You've got pulled pork and chicken, and sides that people (including kids) are equally likely to want. That's kind of important.
So let's say it's 50/50 when it comes to people that want pork or chicken (it never ends up being that, but it's a great place to start). You begin with:
Chicken * 160g * 50 / 1000 * 2.2 (conversion) is 17.6 pounds
Pork * 160g * 50 / 1000 * 2.2 (conversion) is also 17.6 pounds
Important: I don't know if your chicken is bone-in or not, if it's bone-in, add a third back into that number.
So say about 17 1/2 - 18 pounds of each protein. Ordering 20 of each isn't a bad idea.
Now let's calculate your sides assuming that people will want 3/5 of them regardless of what protein they want. That's simple, or 3/5ths of 100, or 60 grams per person of each. Do the math and the conversion and you get roughly, 13 pounds of each side.
Now again, factor the kids in. Kids aren't usually wild about potato salad, and if you're expecting a lot of them, ramp up on the mac n cheese. Likewise, if you know the crowd you're serving isn't really fond of things with gluten, ramp down on the mac n cheese. I wouldn't mess with your protein portions too much based on kids, it's better to have a bit extra and send food home with people than run out.
It's important that people RSVP and indicate any food preferences, allergies, etc - MAJORLY important if someone has a peanut allergy (make sure the folks preparing your meat know if that's the case). You may also find out that you need a lot more chicken than you thought.
In most cases I really recommend letting a caterer handle it, but it's not rocket science (in fact it's more guesswork than actual science). Make sure you handle the food properly (at 100 guests plus, did I mention that a caterer might be a good idea?) I don't know what's in your potato salad, but it needs to stay cold. Do you have the needed chafing dishes to do this, both hot and cold?
I never was responsible for banquets, though I did a lot of cooking for them to whatever amounts were needed - I have a lot of respect for banquet cooks and chefs because it really is an entirely different animal.
What I've done in these cases myself in the past is use this reference chart to get a rough idea of starting quantities per dish. In terms of the actual number of servings I always count a full serving for anyone over 12-ish years old and half a serving for anyone younger than that.
After you've done that, you obviously still have to recalculate to account for the number of different dishes in your menu. As a rough guideline I take a total of (per person):
- 350-500g of "primary" dishes (meat, fish, veggie), depending on if they contain sauce or vegetables inside the dish.
- 350-500g of "side dishes" (salads, warm vegetables)
- I don't account for bread or sauces served loose
This gives you an adequate amount of food in total, while also ensuring that even the most popular item on the buffet survives the first round. If the resulting shopping list goes over budget, add a couple of different soups to the menu and reduce the amounts of solid foods.
Still only a rough guideline of course, but I hope it helps.