  We introduce and study a minimum two-orbital Hubbard model on a triangular
lattice, which captures the key features of both the trilayer ABC-stacked
graphene-boron nitride heterostructure and twisted transition metal
dichalcogenides in a broad parameter range. Our model comprises first- and
second-nearest neighbor hoppings with valley-contrasting flux that accounts for
trigonal warping in the band structure. For the strong-coupling regime with one
electron per site, we derive a spin-orbital exchange Hamiltonian and find the
semiclassical ground state to be a spin-valley density wave. We show that a
relatively small second-neighbor exchange interaction is sufficient to
stabilize the ordered state against quantum fluctuations. Effects of spin- and
valley Zeeman fields as well as thermal fluctuations are also examined.
