what contributes to the temperature of a vacuum
It really depends on how the vacuum is defined. If you, for instance, pump all the air out of a steel container, you will have a vacuum in there. Yet, there will be photons constantly radiated off of the walls. This interplay of photons will be in thermal equilibrium with the walls and therefore will have a contribution to the temperature. For instance, if you would place a thermometer inside this container, the material of the thermometer would be hit by the photons of the container wall and therefore the thermometer would give a temperature equal to the temperature of the wall. As a matter of fact, even in the deepest of deep space, there is some radiation to be found which gives a temperature of about 3K. (This radiation is left over from the Big Bang)

Nevertheless, if you make a true vacuum inside some container of which the walls are at 0 K that cannot be penetrated by any kind of radiation or matter, then the temperature therein is 0 K.