[burriko]

Even easier is Marco Arment's suggestion of using a standard 6x10 bubble envelope.

http://www.marco.org/1131994352

[StrawberryFrog]

Came here to say the Uk version of that: an A5 padded envelope from the post office. It's not that durable, lasting about a month the way that I throw it in my backpack, but it costs under £1.

[jonhendry]

I use one of those, inside a stiff cardboard envelope as is used for mailing things that shouldn't be bent, like photos.