Because it is a side dish, you need just 1/2 pound whole watermelon per person. A 1/4 sheet cake= 9x13= about 15-16 pieces. You will need pizza for 50 (see quantity tables) plus about 40 dogs- some leftovers, but everyone gets their first choice. Chips 1-2 ounces per person (depends on length of party) plus 1/4 to 1/3 cup sauce. 2 gallons ice cream. I might skip either the cotton candy or the pop corn, we are venturing into throw up combo territory with this menu...