bagels- assuming the regular size, 1 1/2 (3 halves) per person
lox- 1 pound per 6
cream cheese- 1 pound per 8
tuna salad, 4 gallons per 100 (how much tuna depends on what you add- do a single batch with a small can to figure this) or if ordering, order by gallons...
egg salad, same as tuna- you need 150 eggs per 100
If people tend to eat more tuna in your neighborhood, order/make a gallon extra

coleslaw, about 40 pounds (5 gallons)

tomato slices, 24 pounds
pickles, 2 gallons assorted
olives, 2 gallons assorted
cucumbers, are you making a cucumber salad of some kind? you need about 3 gallons per 100, which takes about 12 pounds of cucumbers per 100. Just sliced, about 1/2 that

fruit platters- see the fruit tray page

You might want to add:

Jam or preserves, 3 quarts

challah or rye bread or pita- about 12 pounds

Some kind of quiche. This can be done in individual cupcakes or tarts, served room temp.

If there will be a lot of kids, you might consider adding peanut butter to your spreads.