If you eat expired chips, they may make you sick or cause a stomachache because of the bacteria that they are carrying. Before eating any form of food or snack, it is important that you first check for the expiry date. If the food has expired, throw it away instead of eating it.
They may be a little stale but if kept enclosed probably ok because of preservatives. The bacteria comes from your hands going into the bag. That is why it is best to pour out the portion you need and tightly enclose the bag.