Size and weight limits are listed on your airline's website.

Flew from Anchorage to Seattle to climb Rainier this July. I put my fully loaded pack inside a duffel bag and packed other items around the pack inside the duffel. I flew Alaska Airlines and was a little over 50lbs which they didn't charge me extra. My carry on was a daypack that I had extra gear in. I would not recommend attaching extra things to a pack... you risk damage or loss.