As someone who has worked for museums and archives before, I can offer a few things about this.
Museums and archives all have Collections Policies (if they don't, shame on them), which specify the parameters of what they will accept in the way of donated collections, as well as what types of items they are actively seeking. Just ask the archivist for a copy of their policy. They also can and do cull through donations to get rid of things that might duplicate what they already have, or does not fit their Collection Policy. Sometimes, this means throwing out with the garbage things that someone spent a lifetime collecting thinking it would be important. It might be important to one museum, and not to another. All of this is due to space constraints and the time constraints to properly catalog and manage the collection. The person making the donation should know this upfront before signing the donation agreement, and can work with the Archivist, Librarian, or Curator ahead of time to avoid any hard feelings.
Photos and slides are almost never thrown out, as they are usually the most utilized part of any collection by the public. Timetables and other ephemera would probably be welcomed, unless they were a duplication of the collection. It is difficult to determine what an historian in a hundred years might need in the way of research, so often the archivist must simply guess. More often than not, the archivist will err on the side of caution and keep the item.
It would be nice if the museums could publish their policies together, but until that happens, just consider the places where it makes the most sense to donate a collection or part of a collection, such as, stuff related to a California railroad probably doesn't belong at a museum in Golden, Colorado. If an owner would rather have the cash, as opposed to any possible tax write-off, sell anything worth any money to another collector.
Not everyone will have the chance to parcel out their collection as they see fit, but it helps both the individual and the museum to have some planning beforehand.
J. B. Bowers
