No. Opening your bag is NOT allowed. It is your responsibility to keep the medicine or food items
outside your bag but inside the locker.When I gave the exam I was unaware of this rule and had
kept my snack inside the bag. During break I opened my bag, as soon as I took the snack the
proctor stopped me and told that she will have to contact GMAT officials to see if I can continue
the test. But I argued saying I was unaware of this rule and none of the proctors at the center mentioned
before. Finally she agreed. But yea, bottomline is do not touch your bag. You have to keep food outside your bag.
Hope this helps.