Once you have confirmed your appointment. Checking the Institution’s web page to confirm what are the rules and supplies that you can bring into the reading room.
In general, most institutions have lockers to store larger items and have some equipment that helps with working through the material. Prepare to lock up anything that is bigger than a sandwich bag in a locker.
In some cases, if you have the jacket on, you are not allowed to remove it once inside the reading room. Bringing your own notebook is not advisable. It is protocol for most Special Collections to go through and then stamp every non-archival paper you bring into the reading room.