Stacking means earning more than one reward on a single purchase. You pay once, but the purchase passes through several layers: the right card for the category, an issuer offer attached to that card, and a store or portal reward on top. None of the layers is complicated on its own. The value comes from lining them up on spending you were already going to do.
Start with groceries, the most common stack. In a quarter when your Freedom Flex earns 5 percent on groceries, that card is the base layer, on up to 1,500 dollars in purchases per quarter once you activate. A store loyalty account is the second layer, adding member prices or points at no cost. An issuer offer, such as a statement credit for spending a set amount at a grocery chain, is the third layer, but only if you enrolled before shopping. The Amex Gold Card plays the same role year-round at real supermarkets, earning 4 points per dollar on up to 25,000 dollars per year, while warehouse clubs do not qualify for that rate.
Gas stacks the same way with different layers. The Costco Anywhere Visa card earns 5 percent at Costco fuel stations and 4 percent at other eligible gas stations, on a combined 7,000 dollars per year. The first layer is the card rate, the second is Costco's already-low pump price, and the third, for Executive members, is everything else in the trip, since the in-club purchase that follows earns the card rate plus the Executive reward. In a quarter when a rotating card offers 5 percent on gas instead, that card takes the base layer and the same logic applies.
Travel has the richest stacks, and the most traps. Booking through a card portal can add a portal earn rate on top of the card's own rate, and a hotel or airline offer can add a third layer. But a portal hotel booking usually does not earn hotel points or elite nights, so if you are working toward status, the stack that looks richest on paper can cost you the night credit that matters more. The rule is simple: stack only the layers that do not cancel each other out.
Three cautions keep stacking honest. First, issuer offers almost always require enrollment and sometimes activation, and an offer you forgot to enroll in pays nothing. Second, terms change, and some tactics that used to work, like buying gift cards purely to trigger a bonus, can violate program terms. Check the terms before you try anything that feels like a workaround rather than a purchase. Third, never spend extra just to complete a stack. A bonus that made you buy something you did not need was not a bonus.
The practical version is deliberately boring. Pick one base card per category and leave it there. Enroll in the issuer offers for stores you already visit. Join the free loyalty programs for those stores. Then shop normally and let the layers add up. Two or three layers, tracked loosely, beat a five-layer stack you abandon after a month.