We sell plastic gift cards that can be loaded up with shop credit, time and time again.
They work just like a pre-paid credit card. You don't have to spend it all in one go and theres no time limit on when you have to use it up.
If your card is registered, which you can do when you visit the shop with your card (we need to scan it), anyone can add to your credit over the phone or in person, like, when you have a birthday or something.
Terms and conditions apply, but not many. Ask a member of staff.