Suggest you don't try to do a pig roast day of- too many possible mishaps. Pulled pork is popular this year, and I have to remind that you will probably have some non-pork or non-meat eaters in the group, so the menu has to have an option for them. This could be a few pounds of vegetarian sausage such as Field Roast, or it could be a dairy rich side dish such as scalloped potatoes, mac and cheese, etc.

pulled pork BBQ- serving with buns? 1 pound per 4 people, 5 buns or 12 slider buns per pound
6-8 pounds sliced onions per 100

Baked beans- 4 #10 cans per 100 (3 gallons)
Potato salad- 40 pounds raw potatoes (4 gallons made) per 100
Cole slaw- 2 1/2 gallons per 100
Consider adding a specialty salad such as corn relish, broccoli cauliflower, cucumber in sour cream, tomato caprese, etc, about 2 gallons per 100
Rolls- as above. It comes out to 12-15 pounds per 100
BBQ sauce- 1/4 cup per person- about 3 gallons

Tea- about 12 gallons, 1/3 unsweetened
lemonade- about 12 gallons

Also, it is important to have a appetizer plan and this is why:

Before the Buffet; Why You May Need an Appetizer Table
A self-catered buffet is a real challenge to the organizers, and things don't always come together as smoothly as hoped. By planning and setting up an appetizer area or "nibble table" which is ready when the guests begin to arrive, the cooks and servers have time to complete the arrangement of the dinner buffet. This is especially critical if there are children among the guests, or there is a wait before dinner, as at a wedding reception.

This does not have to be complicated. Three items, plus a punch, or two if one is alcoholic, are sufficient. Typically, include a fruit tray, a cheese tray and an attractive dip or spread; or you can go with a dinner theme such as TexMex with chips, salsas, Texas caviar and guacamole; Italian with bruschetta or antipasto; maybe shrimps or other cold seafood, if budget permits.

One appetizer service area serves about 100 guests.