Good call about going carry-on. I always try to remember that there are just two basic categories of luggage: carry-on and lost. If they quibble about the plastic knife, just leave it at the security point. Annoying, I know, but replacable with ease.
I have bought lots of things online but there are two things I wouldn't buy sight unseen and untested:
The first is a backpack -- unless I had tried on and tested the absolutely IDENTICAL model.
The second is boots or walking shoes. In the case of boots/shoes, even trying on an identical...
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