Gift Cards (and Gift Certificates) can be used in EVE. Cards can contain a Mag Stripe and/or Barcode depending on your requirements. The Mag Stripe/Barcode simply contains the unique card number - i.e. no credit information is held on the card. When you sell a card to a customer, you assign the card number to them in EVE (by swiping/scanning the card or by manually entering the number) and all credit information is then stored on the EVE database. Cards can be 'topped-up' with credit at any time. If you want, you can claim back the card from the customer when their credit reaches zero and you can then resell it to another customer.
Visit http://www.printingplastic.com/evegiftcards to purchase cards or get more information.