All of our packs must feature quick-release straps as a house rule. With a single free-action tug, it'll be off your back, along with all the weight and encumbrance penalties that come with it.
Of course, you'll need to keep items that you might require in a fight somewhere other than your 'pack.'
We've just noticed that micro-managing the pack to maintain your encumbrance penalties to a minimum is a bit tedious.
