When all else fails, use boxcars.
For 1952, you're probably a bit early for covered hoppers, so if you're handling any sort of grain, then use boxcars to serve your grain mills etcetera. Lumber was also hauled in boxcars. Any sort of assembled goods that would fit into a boxcar would generally be hauled in boxcars, including automotibles--there were open auto carriers too, but many lines ran special two-door boxcars big enough to hold a couple of cars. Flatcars hold really big stuff and bulk loads--including bigger types of lumber. Gondolas are typically used to hold metal products. Hoppers are used for minerals that would be a pain to unload from a gondola and can stand the weather--coal, ore, rock.
In 1952 refrigerator cars were still largely cooled with blocks of ice, but mechanical refrigeration was in use. 36' reefers were still commonplace, because the icing facilities were built with 36' cars in mind and it was easier to continue to build new 36' reefers than rebuild all the icing facilities. Mechanical reefers obviously didn't have that restriction.
While reefers are obviously used for things like fruit and vegetables, meats and dairy products, they were also commonly used for less-perishable foodstuffs like nuts and seeds.