Normally grains, pellets, and fertilizer are carried in larger three and four bay covered hoppers, due to their lighter weight. The only thing besides sand, cement and roofing granules that I know of would be salt. Of course anything can be carried if larger hoppers were not available.
willie
Two bay hoppers are designed to carry the heavier materials that can't be carried in larger covered hoppers. So you'll have things like fertilizer, cement, clay, sometimes gravel, salt, bulk sugar etc.