For an airplane carry-on bag, we use cloth grocery bags.
Take the dimensions and go to several large Supermarkets.
Quality cloth bags usually run around $3-$4
You are looking for good stitching and long handle.
The long handles allow you to carry the bag on your shoulder (freeing your hands) and also allows you to tie the top closed, before you try to stuff it in the overhead storage.
When packing the carry-on, make three separate piles, and pack each in a separate regular plastic grocery bag.
1) Thing you will not touch until after you leave the Barcelona Airport.
2) Thing you will need in the Airports, but not on the Airplane.
3) Thing you need for sure on the Airplane. book, some food, water bottle, warm clothes...
OK...
Pack items #1, very tightly, in a regular plastic grocery bag. Roll it up tight. Add 4 thick elastic bands to the outside. Put it in the bottom of your carry-on.
Pack items #2 in a regular (different colored) plastic grocery bag. Roll it up tight. Add 3 thick elastic bands to the outside. Put it in your carry-on.
Pack items #3, regular (different colored) plastic grocery bag. Roll it up. Add a single elastic band to the outside. Put it in your carry-on.
The elastics are important. The hold the tight form, but allow you to open the bag at security.
While you are at the airport, you can leisurely access Bag #2
When you board the plane, and reach your seat, remove Bag #3, and put it on your seat. Then tie the carry-on handles, store above, and sit down.
A third bag can also be brought on the plane.... a Fanny Pack. Very hands free.
I use this for tickets, passports, travel papers, cash, phone, tablet, camera, pen, Camino book, cough candies, a few med's.
Very accessible.
I wear this for Camino as well.
When we reached Santiago, we bought new grocery bags.
If you send your Back Pack as checked luggage (full or empty), always wrap it with a 30m roll of Saran Wrap (plastic, stretchy-cling wrap). Print an full 8.5”X11” page with your address and phone number in Spain (your Pamplona Hotel). Include it in the final wrapping so it is clear, and obvious where the Airline can get a hold of you.