they do provide a bag when you enter the park. What we usually do is trick or treat for the first hour starting in the back of the park (the Pete's silly sideshow location is great to fill the bag quickly, then we went to Exposition Hall for the allergy items (my DD has intolerance to sugar and milk) they filled her bag to the top there in one stop. We then rented a locker and put the bags inside. We then grabbed another bag and got some candy, just enough to eat through out the night so we didn't have to haul the heavy, full bags everywhere.
If it's enough it's completely a matter of personal choice