In many cases retailers do sell gift cards with a pre-defined amount that is printed on the card.
Ideally it should be possible to scan the barcode of such an item and by doing that, the gift card id AND the amount should be entered and the gift card process should be completed. In addition, if this item is stock controlled, retailers would have an overview of how many gift cards are on hand in their stores.

As a second best solution to this scenario, it would be great if it would be possible to define denominations when issuing a gift card. This way, typing errors can be reduced and the whole sales process is way faster.