Branch line or mainline? If branch line, then you're talking about smaller steamers, like ten-wheelers and smaller. You may see the occasional Pacific (older 4-6-2 relegated), same with 2-8-2s.
If mainline, then you could do the Superpower thing besides the more modern 2-8-2s and 4-6-2s. 4-8-2, 4-8-4s, 4-6-4s.
For diesels, basically F-units and endcab switchers. Alco roadswitchers as of '41. E-units for passenger work.
Freight cars, there's a book published by the NMRA called the Postwar Freight Car Fleet. But, it covers freight cars from 1898 to 1947. Which basically means that depending on where you are, you could see a lot of these cars roaming around. 40yr lifespan, you know.
Book is pricey, $65 for non-members. I want to get a copy eventually, once I find my NMRA membership card....
Kennedy