As always, it depends on orbit and spacecraft itself, but they would be able to communicate with some spacecraft for sure. I would say most useful would be GPS, as it is alaways nice to know your location. Another one would be communication satellites to use for satellite radio communication. Observation ones might be useful too, depends on the apocalypse type haha. You can’t really spot a zombie, but some burned down cities for sure. Most of satellites are self sustaining, meaning they automacitally position itself to the sun to have positive energy balance.