Originally Posted by jmorgans

It is a good idea to buy gift cards in your supermarket to take advantage of double miles, but I don't think there is any advantage to doing it during this promotion. Remember that the card gives you double miles in supermarkets all the time anyway. I don't believe that the current promotion gives you any more than double miles (i.e. it doesn't quadruple your miles in supermarkets). So you can just buy the cards closer to your trip.