Can I offer gift cards without a point-of-sale (POS) system?

Absolutely! One common approach is to sell one-time use cards with a face value printed on the face of the card ($5, $10, $25). An example of this are coupon cards. We also have a number of clients that keep track of balance in a spreadsheet, or come up with other creative solutions to avoid the complexities setting up a new POS system.