In the unlikely chance that Internet is not available at the event.
Paper shopping lists can be used to mark the product "scan" completion and this Excel document can be used to randomize the gift card.
On the "Gift Cards" tab, enter the # of awarded gift cards per value in the yellow cells. This can be found on the admin backend at the bottom in event details.
Go to the "Results" tab and enter the randomized value from cell B4 in blue to the GC Value column. Each gift card awarded should be on its own row and it will calculate the randomization based on available gift cards.