I'm hosting an all-day event for about 50 people. I'd like to have snacks/finger-food out all day, in addition to a light noon meal. As far as finger food goes, I'm thinking veggie trays (carrots, broccoli, celery), bread and dip, and pasta salad. For the lunch, I'm thinking rice and beans, with some sort of sauce.

I would suggest a fruit tray rather than a pasta salad for the AM snacking, and some low fat cheese- people will fade if they don't get a little protein. Also, hummus as one of the bread dips.
1 pound fruit per 5
1 pound cheese per 6-8
2 ounces bread per person, 1/4 cup dip

For the lunch, rice and beans fine, add a green veggie salad, have some interesting sprinkles for the top. A yogurt or custard dessert would be a fine choice to balance the meal.