Refer to my profile banner to see one van that had a generator and storage inside of it. It also has a working big radio and a table and chairs for crews to eat.^That van is in maintenance of way service rather than train service.
Where cabeese are still used these days, it’s mostly to provide a “shoving platform” - a safer option for workers protecting a backup move - so they don’t have to hang off the side of a freight car while the train backs up. Often the doors to the car are welded shut, so there is no access to the interior.
I don’t know what this particular van was doing in your shot, but it’s spring, and the MOW forces are on the job.