I will fly Alaska Airline for a gig and will be likely bringing a carry-on suitcase (medium within their size limits) and a backpack for most gears with me on the plane. Here is the fine prints on their website.
You're allowed one carry-on bag, which can measure up to 10" H x 17" W x 24" L (25 x 43 x 61 cm), plus one personal item, such as a purse, briefcase or laptop computer. At least one of the items should be stowed under the seat in front of you.
I have a medium size Canon Deluxe Photo Backpack 200EG backpack. 15 x 12.2 x 7 inches. It can be bigger after adding my gears. I wonder if anybody have the experience with carrying this backpack as 2nd carry-on item (called one item) on airplane recently.
Thank you very much.

though that isn't stated anyway (which is the real trouble!!) 
