You can go get a copy of my BBQ catering planner from here
you can set the amount per person, the number of people, etc. The planner is a freebie, use it, enjoy it.
It can also be used to calculate costs as well, if you need that ability too!
100 people served 4 Oz per meat per portion will need 46 lbs (uncooked butt) for 100 x 4 Oz portions of pulled pork or 61 lbs (uncooked butts) for 100 x 5.33 Oz portions of pulled pork.
If you count 1 chicken thigh per person, you will be doing about 5 packs of chicken thighs as well as 5 butts at 9+ lbs, (for 46 lbs or 7 butts for 61 lbs).
If you are using #10 cans of beans as Bill says you can serve 25 people per can, so for 100 people you will need 4 cans of beans.