Improved embodiments of a blank for a dunnage plug which fills gaps between cargo and a side wall of a vessel or vehicle in which the cargo or lading is transported include a single sheet, preferably of corrugated cardboard, having cuts or slits, slots, perforations and bends positioned thereon for allowing portions of the sheet to be folded into a plurality of channels which intersect perpendicularly and interlock in a plurality of half cross-lap-joints to provide an extremely inexpensive structure having a designated thickness and being capable of withstanding substantial loads in compression without failure. Since the improved dunnage plug blank of the invention is assembled and disassembled without separation of the sheet into more than one piece, there is no tendency for portions of the dunnage plug to become lost at any time. Further, if the dunnage plug is disassembled it folds back into a single flat sheet for efficient storage. In use, the improved dunnage plug is adapted to be affixed to either a sidewall of the transporting vessel or vehicle, or a sidewall of the cargo.