A flat blank carton is provided for packaging articles or products. The flat blank carton includes a base, a top, and a rear panel, hingedly connected to one another, and pairs of upper and lower side flaps hingedly attached to the top and base panels, respectively. The upper and lower side flaps include locking projections and corresponding locking recesses that are brought into mating, locking engagement as the top panel is folded over the base panel. After loading with products, the front end flaps of the cartons can be sealed to close the cartons.