Personally I don’t like loyalty systems that work just as a discount. The loyalty card promotion I like involves a cross category sale - e.g. buy ten coffees get a free food item or invite to our next cupping session.
Another promotion I recently saw involved giving away 5 coffees that had to be redeemed in a single order. I like this as it gives the customer a chance to shout coffee for their workmates and exposes new potential customers to your coffee.