As organised as we were for our trip last November, the one thing that we forgot to pack was the information that Disney send out a few weeks before you leave which also contains the voucher for the gift card.
I remembered about it as we were half way across the Atlanctic.
We called Disney once we got out there & gave them our booking reference, the chap on the end of the phone had e-mailed a copy of the voucher to me before I'd finished asking if he could do it.
We printed it out & took it the to World of Disney Store.