Can you have a small bag of chips?
You can...there's no reason why a small bag of chips (or a small portion if you have the will power!) can't be part of your caloric intake.
If you restrict, or cut out a food today, while you're on your weight loss journey...when is it OK to reintroduce it?
At some point?
Have a small bag/portion, count it in to your calories for the day, and enjoy - guilt free