Many years ago, when I attended the Archives, nothing they have on line now was available. So a lot of what I suggest is old ..maybe.
Only copy and look for what you DON't have or can get online.
Make sure they will be open during the time you will be there. Weekdays are best.
I stayed at a hotel 1 block down from the hotel that picked up and dropped off to the airport--no car needed.
Take enough $1 bills to feed the copy machine.
I was strictly there for research so I didn't do any touring and the weather was hot.
DON'T FORGET TO STOP research and eat. The same hotel had a restaurant and a sandwich shop was next door.
MAP OUT YOUR research before you go. Now they charge for everything to fly, you have to cut back on luggage.
When I went, the Educable List Room --did not allow you to view books away from the room. I narrowed the list down to the years I KNEW my ancestors lived in the area. These same years 1900's, have not yet been scanned and put on line for Monroe Ms. So ASK for the year you want if it is not online. COPY the page before, you find the household and after. Family lived as close as possible.
Since it has been many many years since I was there, I can better suggest Linda Rudd's advice. The librarians know her as a researcher very well. In fact when I walked in, this information was volunteered to me. We Later met and I can proudly say she is a internet friend who lives in Mississippi.