Cheddar cheese- 1 1/2 pounds grated and
maybe a pound of a second creamy white cheese or mixed cheeses, eg with some blue or pepper jack?
Maybe a pound of cream cheese also
Ham- 10 pounds if for sides, 5 if chopped for omelets
Bacon- 8 pounds for sides, 2 thick slices per person; about 2 pounds cooked bacon bits if just for sprinkles
Mushrooms- 2 pounds sliced fresh raw, or more if cooked
Green Peppers- 2 pounds
Onions- suggest green onions instead of sauteed whites. 8 bunches, chopped.
Red Peppers- 2 pounds
Maybe 2 pounds of sour cream.
Some people like to have olives, 2 cups chopped
And have you considered a sweet omelet option?

What about salsa? 1 cup per 6.