This is where supplies for the train are stored. If you can read the sign, you can see that only Amtrak employees that work in this department are allowed into this area. I assume this is to discourage theft and maintain better control over the inventory.
The photos in this slide show were taken in the mid-1990's by Steve Grande on his Amtrak travels throughout the nation. The size of the photos is purposely smaller as disk space was expensive and download speeds were slower at that time.