Rolling stock refers to passenger cars and freight; in other words, the train you're modeling, unless you only collect locomotives with no layout. Model railroaders of n gauge trains (or n scale, which is the same thing) need a lot of rolling stock in order to make their layouts look realistic. A layout usually consists of 50 to 75 or 100 to 150 cars, and this will depend largely on the size of your layout - the bigger the layout, the more train cars you'll probably want. If you're like me then you'll prefer just a little less than too much. I was originally attracted to n gauge because of the ability to construct larger and /or more elaborate layouts.
With more models to choose from you can definitely find the N gauge rolling stock you need, (the manufacturers understand that us N gaugers are going after larger layouts.) You will need to mix cars, but the longer you mature in the hobby, the more important it will become to you to base this on specifics of the era and the railroad you're modeling. What I'm saying is that you will need to look into the history of freight cars, which will eventually but inevitably become a sub hobby for you, as it did for most of us.
During the 1920s it's ordinary to find wood cars. Between the first and second world war, the freight cars were wooden single-sheath boxcars with steel frames. Hoppers and gondolas were manufactured and later on, steel sheets were used instead of wood. By the 1930s, the wood boxcars disappeared and the steel counterparts ruled the tracks. In 1937 the AAR boxcars were very common. By the 1960s, the steel boxcars were already wearing out and they were replaced with exterior post car trains that came with different paint schemes.
A personal favorite of mine are the refrigerator cars which kept their cargo cool while traveling. These boxcars were basically insulated and tons of ices were used to keep cargo cool. The cars were made of wood and looked like billboards because of their different colors. Later on, steel refrigerator boxes came out. By the 1950s, the larger cars were already equipped with mechanical refrigeration, and by 1970, the ice bunkers were already obsolete.
Gravel, lime, cement, and sand were usually carried by hopper cars. Other variations of the cars also came out which carried plastic pellets, salt, potash, grain, and many other things. Tank cars were also common but through the years has undergone many changes as well. Before, the tank cars could only hold about an 8,000 to 12,000 gal capacity, but the modern ones can now hold around 33,000 gallons. The tank cars can carry different things like oil, propane, solvents, corn syrup, vegetable oil, etc.
During the 1930s, truck trailers were used for long hauls. It was called TOFC or trailer on flat car, and until today, these trailers still exist. It's much easier to develop a model from the 1920s to 1950s rather than creating model railways from the 1980s up to the present. You can enjoy the wide range of choices since this period while the evolution among freight cars took place the most.
Proper selection of the rolling stock should be done with discipline. Carefully study the different photos you can find on your favorite railroad. Always pick the freight cars that suit the era. You will also need passenger cars for the layout, which will complement the freight cars and can create a much more realistic layout. Again, if you're like me, you're layout has sleeping cars, baggage cars, observation cars, coaches, and diners.
Hobbyists should expect plenty more models of rolling stock today and in the coming years.
