Certain specific embodiments disclosed herein include modular building structures that include: a first wall and a first support panel connected to a second wall and a second support panel, wherein: the first support panel is integral with the first wall or is adjacent to and connected to the first wall; the second support panel is integral with the second wall or is adjacent to and connected to the second wall; the first support panel includes two first vertical elongated slots; the second support panel includes two second vertical elongated slots; and a clip having two prongs disposed within the two first vertical elongated slots and two prongs disposed within the two second vertical elongate slots.