i think should sort out who is in to organize the event first.
suggested committee
official representative - 1 person (handle sponsorship, emergency contacts etc.)
manpower (networking) - 2 persons (emails, shift allocation, publicity on forums etc. for volunteers)
manpower (I/C on ground) - 2 persons (to make sure process is running smoothly)
logistics (planning and setup) - 2 persons (keeping an inventory list, allocate equipment on ground)
logistics (food and first aid) - 2 persons (meals and first aid)
donations keeper - 1 person (responsible for donation box, will witness accounting with official representative when passing box to Salvation Army)
treasurer (optional) - 1 person (keep track of expenses, so that everyone can share the monetary costs end of the day)