I have bought several carabiners over the last year, usually from luggage sales shops at the airport. I use them to clip all of my hand-carry items together. There is a special do-hickey for this purpose that came with my Tumi luggage but I keep misplacing it.
Unfortunately, most of the carabiners you buy last minute (like I do) from the airport are crappy quality. I cannot imagine what would happen if someone actually took them on a mountain. Most certainly, they would have a serious accident.
Desperate to find something that would suit my purpose and wouldn’t fall apart easily, I bought a few different ones off of Amazon and am pleased to say that I like the Nite Ize ones very much. They come in all different sizes and you can even purchase a set of sizes at once.
Mind you, these carabiners are very convenient in other ways. If you have a lot of heavy grocery bags to carry, you have probably experienced them cutting into your fingers. You can use a large carabiner, instead, and save your flesh.
I sometimes clip whatever I’ve purchased at Duty Free onto my carry-on and let everything simply hang off of it, while it all takes a ride on my wheely bag.