One of the foundations of a relationship is deciding where you stand on crucial things like physical boundaries. Will you eat out of the same bag of chips on your first "date"? Will you drink out of the same cup when you are engaged? These are legitimate questions that need to be addressed before they become an issue.
A few things to consider as you make your decisions:
1). Since food is the way to a man's heart, you need to be extremely cautious with food. Think about it. You touch the potato chip that he's going to eat. Your hand oils get on it and pretty soon you are on your way to his heart. Okay well... maybe only your hand oils... but still. You should think.
2). You shouldn't just do what seems easiest, but what is right. Yeah... it probably is easier to just share a cup. Less dishes, right? But you have to think. Do I really want to go that far, that quick?
3). Avoid all appearance of evil. If you both reach into the chip bag, people might assume that you are holding hands. So if you decide to both eat out of the same bag, either get a clear one or wait until the other person has grabbed their chips.
Make your standards first, make them your own and hold to them. That's how you'll weather the storms in this chip bag saturated world.