USPS medium flat rate box.
You can fit 6 small flat rate boxes into a medium flat rate box. Put one rack of chips, padded, into each SFRB, with one small box just filled with padding. Tape the the top and bottom of the box, then tape around the side of the box to secure the top/bottom tape and to reinforce the glued edge of the box to prevent splitting.
No better way to ship chips, imo.