I've been building some perimeter stringer blanks using various combinations of carbon, wood and foam. Invariably a small piece of bag will get caught between the foam and stringer, such that debagging the board tears a hole in the bag.
Dennis scored me some polyethelene food grade bags on the cheap. The work perfectly for assembly work and are sealed on three sides to minimize potential leaks.
My guess is that there are TONS of alternatives to high priced bagging consumables.