Complex sentence: Generic cerealine was one the three most popular cereals of the time, along with cracked wheat and oatmeal, all three of which were typically sold by retailers who bought cereal in barrel lots, and scooped it out to sell by the pound to customers.
Split into simpler sentences: Generic cerealine was one the three most popular cereals of the time, along with cracked wheat and oatmeal. All three were typically sold by retailers who bought cereal in barrel lots and scooped it out to sell by the pound to customers.