A happy event. I would count this as 75 (3/4 of 100) unless all the kids are teens.

This looks like too much food and more choices than you need. For example, a 6 foot sub is usually counted as 25-30 servings, so you have at least 60 servings right there.

If it were my party, I would consider tweaking the menu to simplify. Even if you make all these cuts, you will still have some leftovers.

Chips, 1 pound per 12; dip/salsa? 1 pint per pound of chips
cheese and crackers- 1 pound cheese per 15, about 5 pounds crackers
maybe add a few quarts of olives and small pickles?

Salad- How about doing antipasto style marinated veggies or gardiniera? You would need about 2 gallons. You can buy this jarred, which saves a lot of refrigerator apce, or make it yourself, a couple of days ahead:
www.ellenskitchen.com/bigpots/appetiz2.html.

15 ft hero (5-Italian 5-American 5-grilled chicken) already sliced- already more than 60 servings!
Sliced Italian heroes- skip entirely

Baked ziti - no meat
Mac and cheese
I would do only one of these- any kid will eat ziti, or the chicken and pasta- no more than 6 pounds total dry pasta with the second pasta dish below

string beans- about 15 pounds, these could be served room temp

Grilled Chicken/ broccoli and pasta in a garlic and oil 4 pounds pasta, 6 pounds broccoli, about 12 pounds chicken
Sausage with peppers and onions about 12 pounds sausage, equal amount veggies
Chicken nuggets for kids- poor kids- you know, they will happily eat the sandwiches and the grilled chicken from the pasta- you could skip these...

Rice- skip entirely. Just have some good Italian bread, dipping oil and butter.

With your desserts and fruits this will make an ample meal. If you put the pre-made refrigerated casseroles in the oven before you go to church, they will be ready to serve when you return. Tightly covered, 325 oven. They just need to get to 165 at the center of each dish. With your pre-made sandwiches, you could be ready to serve almost immediately on return.