Heres a piece thats both durable and delightful.

Save Your Carry-on Charges

• Bag size 18 x 13 x 6.3 inch fits personal item size 18 x 14 x 8 inch of Spirit Airlines & Frontier Airlines perfectly, which can be placed under seat and no need to pay carry-on.
• The bag could be foldable into its own small pocket when not in use, but no extra small bag is included. Folding up into a small pouch does not take much space in your luggage, unfolded as extra bag for souvenir or clothes when travelling leaves room for valuables in your suitcase, or used as a carry-on with decent size to fit under an airline seat or in the overhead bin in case you are overweight for a checked bag.

The kind of thing that makes you think, This is exactly what I needed.