The problem with offering some vegetarian is that everyone has a different idea of what a vegetarian will and won't eat. Some vegetarians will eat fish, some won't. If you can change your order why not go with some egg salad, turkey or chicken, ham, roast beef, cream cheese, salmon or tuna salad for a total of 40 sandwiches? If your budget will allow it why not have a platter of raw veggies such as carrot sticks, broccoli and cauliflower with a dip?
You don't mention the bread you are using but it's a good idea to have both whole wheat and white bread sandwiches.
Just keep in mind that you can't please everybody.
A friend of mine often makes sandwiches for her church and when she does egg salad she makes some sandwiches with onions and some without.