One organizer collects a share from everyone chipping in, into one visible place, and the venue, catering, and decorations come out of that table. Collect before you book so nobody fronts the deposit.
A graduation party often has a few families or friends going in together: a venue, catering, a photographer, decorations, all landing at once. One person ends up booking it and fronting the deposits, then collecting from everyone else in the weeks around a busy graduation season when nobody's checking their messages.
A graduation party has a long tail: the extra tables, the cake, the day-of supply run, sometimes a group gift for the grad on top of the party. Instead of one person fronting each one, collect a little extra into the table so those come out of shared money too.
Whoever pays for a party cost requests that amount from the table, the organizer approves it, and everyone sees it come out. Nobody keeps a side tally during a busy season, and the leftover is on the record to send back or put toward the grad's gift. (Combining it with a milestone birthday the same summer? See collecting for a group birthday party.)
The organizer holds the money the way one person always does, only now everyone sees every dollar. It goes through Stripe to the organizer; TableCash never holds it and is just the record.