The NFL has requested teams put a restriction on the type and size of bags fans may bring in to the stadium on their game days. Here is a picture of the bad and all the info where you can get one.
Bags that are allowed are clear plastic, vinyl or PVC and do not exceed 12 in x 6 x 12 in
One Gallon clear plastic freezer bag (Ziploc bag or similar)
Small clutch bag can be used but they have to be approximately the size of your hand.
Here is the full policy.