Amtrak's older car designs didn't leave much of a place for the train crew and support staff to leave their personal belongings or do their paperwork, which is why, in many cases, you see them occupying various seats and tables. Even the newer designs, like Acela, don't always factor in all the different crew members' needs--either that, or Amtrak just planned to set aside regular seats and tables in the train for them to do their work.

Amtrak train crews consist of the following crew and staff members, and I've briefly listed their job descriptions:

1) Train crew in train service--conductor, assistant conductor (aka brakeman): responsible for the overall safe operation of the train. Train cannot move without their permission. On some runs, they communicate with the train dispatcher and copy track warrants, slow orders, track work orders, notate signal indications, and the like. They're also responsible for collecting tickets and ensuring passenger's compliance with laws and Amtrak policies. Their word is final on the train, and they have every authority to kick someone off the train or even have them arrested, if necessary.

Single-level trains especially don't really have a dedicated place for the conductor to copy track warrants and other forms, so you'll often find the conductor grabbing a table in the diner or cafe car.

Acela has a dedicated conductor's office in the cafe car, where he and his paperwork hangs out, although the engine can be accessed without exiting the train, so he'll often head to one of the locomotive cabs in between stops.

Long distance bi-level trains with transition dorm cars have a work area where the conductor can spread out his paperwork. You may see conductors in the bottom of the Sightseer Lounge occupying a table if they want to be closer to the rest of the crew, as the trans-dorm car is usually at the very front of the train.

Conductors usually work either day-turns or, at most, have a single overnight layover before returning to their base, so they tend to pack like pilots and don't require a lot of room for their personal belongings, which they can either stash in the locomotive cab or at whatever table they've commandeered.

2) Train crew in engine service--engineer, assistant engineer (aka fireman): drive the train itself. On most long-distance runs, where there are two engineers in the cab, they take over the responsibilities of communicating with the train dispatcher.

These guys usually stay in the engine, and there's ample room in the cab for their paperwork. They also work either day-turns or overnight-and-back trips and so don't lug around a lot of stuff.

3) Lead Service Attendant: the (sort of) supervisor for the on-board-services staff, but primarily responsible for the dining car. He or she monitors (and is held personally responsible for) the inventory of the dining car's supplies and the cash taken in, which involves paperwork.

Since they work in and are responsible for the diner, and there isn't really any place they can spread their inventory sheets and store their stuff other than at a table in the diner. Unfortunately, this reduces the capacity of the diner, but without their own work alcove, there's not really any way around this, so yes, it's SOP.

LSAs work from one end of a train's run to the other, so they tend to carry more stuff (changes of clothes, stuff for their off-duty times, etc-they may work upwards of six days in a row (three out, three back on some western routes) before returning to their home base. On long-distance (overnight) runs, they are assigned a roomette in a specified dormitory car where they crash in the few hours between dinner and breakfast. This provides them with a place to store their bags and personal items.

4) Cafe attendant: monitors the inventory of (and is held personally responsible for) the cafe car's supplies and cash taken in, which also involves paperwork.

His or her personal belongings can usually fit in the cafe alcove (or a storage closet nearby), and he or she can do the inventory from the cafe, so not much extra room is required. Sometimes you'll see them borrowing a table in the cafe/lounge (next to their work area) to work on paperwork, though.

Like the LSA, they work from end-to-end on a route, but they're also assigned a room to sleep in and store their stuff in. During their breaks, they may head up to their dorm room or hang out in (if on a longer run with a trans-dorm car) the staff break area, where you won't see them.

5) Train attendants (diner, sleeper, and coach): oversee specific cars (or sections of a dining car) and are responsible for the safety of the passengers in those cars. Also provide services to the passengers of those cars (more so in sleeper class--turndown service, beverage service, etc.) and may be responsible for assigning seats (in coach class).

These guys don't have much in the way of paperwork to do, since they're there primarily for passenger safety and comfort, so their stuff stays up in their dorm room (if they're on an overnight run--like other OBS staff, they work train runs end-to-end). They still need a place to sit and watch over their car, though, so they'll usually grab the last seat pair in a car to sit, do crossword puzzles, read magazines, or whatever while they're on duty. If they're on a shorter run, they'll stash their bags in this seat, too. This is SOP, too, since there's not really a designated attendant seat or work alcove. These guys will also often head up to the trans-dorm car and hang out in the staff break area (if available) or at the designated staff table in the diner/cafe (less kosher, but usually acceptable) between stations.