Needed to get camping gear to the Rockies via airlines. There would be no room for the bulk of a suitcase in the rental car and all our duffel bags were used. To solve this problem two used priority mail boxes were fitted open end to open end. The box overlap was adjusted to fit the contents and taped in place. A handle was made by rolling a narrow strip of corrugated cardboard and taping it in a small diameter tube. Twine was fed through the handle and around the box.
The handle prevents the twine from cutting your fingers when carrying it between the car and baggage check.
After arriving the Rockies the boxes were folded flat and stored nicely in the back of the rental car. The twine and handle were saved and reused.
Note the 'baggage' stickers on the box. The baggage clerk said this was important to make sure it was not mistaken for mail and sent back home. It would have been a bad situation if the camping gear was sent home before arriving in the Rockies.
The $1 suitcase worked great, it will be used again.