What can I put with two African dwarf frogs in a 2.5 gal tank?

You shouldn't put any other animals in the tank as that will overcrowd the tank. ADFs are not particularly susceptible to overcrowding, but they will be when fish or other animals not of the same species are added. They are not very active animals, but are exciting to watch when feeding as they are voracious eaters. They are susceptible to standard water-borne illnesses.