I've done everything from paying for group t-shirts to sports teams to shared vacation homes and I've never thought the problem was hard enough to need an app for it.
1. Divide food bill between number of attendees
2. Divide drinks bill between number of drinkers
3. Each individual adds 1 + 2 and ponies-up accordingly
Apologies if I have misunderstood.
Add up what you ordered, write name of card you are using to pay on the back with the amount. Pass the check to the next person.