BTW, is it a pilage bag or pliage bag? Where can I find one? Can it be ordered?
potiron, I never close my birkin, even when going through security. The leather is stiff, so it takes a little effort to close it; also, because it's stiff, the top tends to stay closed all by itself, and the bag is deep, so the result is that stuff doesn't fall out.
I wouldn't carry box onto the plane. It would just get too banged up. For this purpose I have a 45cm togo Birkin as a carry-on. You'll probably be horrified to know I kick it under the chair.