Q. I have a credit from an unused Delta flight that expires at the end of May and I don't think I will be able to use it before then. Are there any other options for applying that credit to something else, such as a membership to the airline’s club lounge or buying duty free on board?
A. There are two types of Delta credits: Delta Dollars and Delta e-credits. The former are given as customer courtesies or for oversold flights; the latter are for refunds or price differentials being credited to an account. Delta Dollars cannot be used to pay things like SkyClub passes or duty-free purchases, but they are eligible to be used to buy a ticket for someone else.
E-Credits rules vary and are typically non-transferable. They cannot be used for SkyClub or duty free purchases either. So basically no, you cannot pay for things other than air travel with them.
But there is a somewhat sneaky way to prevent your credit from expiring, and it’s perfectly legal. Buy a fully refundable ticket with Delta for a future date of travel (perhaps December) on a trip you think you may be taking. Pay for part of it with your credit and pay the rest with a credit card or cash. If you can take the trip at that time, great. If not, simply change that ticket (since it's refundable and changeable without penalty, but better make sure it is when booking!) to a new trip you would like to take on Delta. This should preserve the value of your e-credit if done properly. Remember, this will no longer be an e-credit, but an actual flight reservation that you can either use as is or modify at some future point. Since the fare is fully refundable, if you decide you don’t want to travel at all you can simply ask for a refund in the form of your original payment. This strategy works with all airlines, not just Delta. While it’s true that fully refundable fares are more expensive than non-refundable ones, the thing to keep in mind is that if you don’t use the ticket you get your money back.