Are you doing whole chickens or pieces? I did a gig for 125 last month and did 150 pieces of thighs and had about 25 pieces left.
WHen I do ribs I figure that 1 rack of spares will feed 2-3 people if I'm dealing out the ribs at 2-3 bones a piece depending on the rack. So if your getting your ribs from Sam's in the 3 pack, your going to need at least 6 packages if not 7 to be on the safe side.
I'm sure others will give their advice , but if it was me doing the gig this is what I would plan. Hope this helps.
Peoria Custom Pit 24x72*Treager Texas Style Smoker *Whole Hog Country Smoker*
" You can put all of the sauce on it you want, but you still have to master the art of cooking barbecue"
- Mike Mills-