The triple sandwich is a format defined by retail rather than by a filling. It is the chilled three-piece pack: three sandwich halves, often two or three different fillings, sealed in a wedge-shaped carton and sold as a single unit, usually as the centre of a lunchtime meal deal. The defining fact is not what is inside but the structure and the economics around it. A triple is engineered to be assembled in a factory in the morning, hold its shape and stay safe in a chiller for hours, survive being carried back to a desk, and still read as fresh when it is finally opened. Every choice in it serves that brief.
The craft is preservation and proportion, solved at scale. The bread is a soft sliced loaf chosen for how slowly it stales in a sealed wedge rather than for flavour, and the fillings are bound, not loose: mayonnaise-set tuna, egg, or chicken that will not migrate or leak through the crumb over a long sit in the cold. The fillings are spread to a measured, even thickness across the whole slice so that every one of the three pieces is the same from corner to corner, because an uneven factory sandwich is the one complaint the format cannot afford. The wedge carton does structural work as well as marketing: it braces the soft triangles so they hold their shape and do not crush in a bag, and the multi-filling layout exists so a single pack does not become monotonous before it is finished. It is the lunch counter problem of the cheeseburger solved by refrigeration and a sealed box instead of a hot pass.
The variations are the meal-deal menu itself. The all-day-breakfast triple, the chicken-and-bacon club layout, the mixed pack that pairs a tuna with an egg, the cheese-ploughman's wedge: each keeps the three-piece, bound-filling, chiller-stable architecture and only swaps what is inside. The doorstop and the builder's sandwich are the opposite instinct, generosity over engineering, and are treated on their own. Each deserves its own article rather than being crowded in here.