In 1980 I flew from Pennsylvania to California to work as a professional trail builder on the initial construction of the Pacific Crest Trail. I had a carry on bag and a check-through backpack B/C I would be camping when working.

To cover the backpack I just used a white canvas laundry bag with my name & address on it in permenant marker. Worked fine. A military surplus duffle bag would be good too.

Eric
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"There are no comfortable backpacks. Some are just less uncomfortable than others."