Abstract: The invention relates to building a rucksack. The bag is made of first material panels, notably fabric, complementary panels made in at least one other material being laid out on the bag. Assembling devices are laid out between the first panels so as to form housings which are all grouped together and into which are introduced the complementary panels and a single and unique cuttable border closing the housings; severing of the cuttable border allows the housings to be opened for extracting the complementary panels.