I just bought a good old LeSportsac bag that will be perfect as a carryon for airlines that have tiny carryon regulations. The Deluxe Medium Weekender is what I got, and best of all the narrow depth is perfect for Iceland Air as it is only 7.5 inches. The depth is what is often the issue with some carriers. The overall dimensions on this are 11.5" x 15.5" x 7.5" . There is also a large bag, which is 13.75" x 19.75" x 9.5". So you could squish that down if it were not stuffed, but I got the medium and it should be perfect. It is only 1 pound, and the interior is sort of a champagne color, which is nice because then I can find things vs a big black hole;) The pricing varies by design, but this particular one is $125, but they have a 20% off Mother's Day deal right now.
This bag will go to Iceland with me this summer and I will throw my empty daypack into it. We will be having a camper van, so I do not want to take a regular suitcase since this will be easier to squish into an area in the camper. I think I will test it out next week on a short trip to my moms, just to get a feel for it.