Several weeks ago our library experienced a power outage during open hours, and staff were compelled to resort to circulation procedures from the Dark Ages, i.e., hand-writing the barcodes from each patron's library card and from every single book they were checking out.
I thought that there must be some barcode apps out there that could 1) capture and store a string of barcodes, and 2) export the stored data via email. After downloading seven or eight free candidates and trying them out, the "winner" was the Bar-Code app. It is admittedly still somewhat clunky, but it would nevertheless be faster than writing dozens of barcodes by hand. I've introduced it to a handful of our staff, so that in the event we experience a similar situation at least one pair of hands could be scanning cards and items with the library iPad.