Flatten the part of the bag above the chips as much as possible.
Fold both corners over like this.
Flip the bag over so you are viewing it like this, making sure the corners stay folded.
Begin rolling the bag somewhat tightly.
Roll until you reach the chips.
Pick the bag up so you are viewing the front of it again, keeping it rolled tightly.
Fold the corner over like this.
Do the same with the other corner.
The folded corners should keep the bag closed until you are ready to open it again!