I use one of the tiniest models available: KINGMAX Super Stick . Other manufacturers also have similar models. And there are card-readers for micro-SD of similar size.
The size and weight are extremely small — perfect for EDC, but the problem of finding the right place for it had to be solved. So I looked at stuff I always carry with me and found a fold in my wallet.
The last ingredient — velcro to attach the drive. For such a tiny drive it more than enough.
Step 1: Materials
tiny USB flash drive
piece of velcro
thread, needle and a thimble
Step 2: Wallet Side
Step 3: Drive Side
Step 4: Done
(There are two different drives in photos. I used the white one for more than a year and was completely happy with the storage system. Recent upgrade of the drive and the wallet gave me the possibility to repeat the work and made this instructable.)