I'm planning on buying a Keepall soon but I am SO TORN between the 45 & the 50! I think for weekend trips in the car, I'd rather have the 50 to get a little more space. I don't think I would use Keepall as my main carry on for plane travel, but I would love it though if I could use a Keepall as my "personal item" on the plane, to stuff under the seat if it wasn't super full. Do you all think the 45 would fit, or have you used it that way before? I just want to make sure I pick the most versatile choice! Thanks