A large number and variety of industries profited by the increase in automobile ownership that consistently occurred from the 1920s to the present. For purposes of discussion, this answer will focus on the explosion in car ownership that occurred between the 1920s and the 1970s. Beyond that time period, the basic dynamics associated with the automotive industry and the vast service sector that grew to support manufacturers and owners had already been well established.
The first beneficiaries of the increase in automobile ownership, of course, were the car manufacturers themselves, which evolved into massive operations incorporating tens of thousands of square feet of plant space. The demand for cars spurred growth in the manufacturing sector, but also precipitated considerable growth in the spare parts industry, as well as in the automotive repair sector. Demand for cars obviously drove the oil industry and made it among the most lucrative in history, creating jobs in the drilling, refining and distribution sectors, all major components of an economy. In addition, an enormous infrastructure was created to support the American love affair with the automobile. Roads, especially the construction of the interstate highway system, initiated under President Dwight Eisenhower, were built to facilitate the movement of automotive traffic within and across state lines. Roadside restaurants, motels and service stations sprang up along the almost 47,000 miles that comprise that highway system, accounting for hundreds of thousands of jobs, not including the construction workers who built all of these restaurants, motels and service stations.
Closer to home, in terms of the automotive manufacturing and service industries, the demand for cars throughout the 20th Century created a market for services oriented towards the tens of thousands of workers employed by the automotive companies. Bars, restaurants, and other service industries invariably emerge to profit from the paychecks of the manufacturing employees. In short, the rise in demand for cars throughout the United States, as well as in other countries, facilitated the development of thousands of jobs in a variety of economic sectors that came into existence for the purpose of profiting off of the increasingly mobile population.
Steel and oil industries were helped greatly by automobile manufacturing.
Tourism and was also helped by increased automoblie ownership. People now had the ability to travel greater distances and were more willing to do so. Going on vacations, weekend trips, and sunday drives were now all things average poeple could do. As a result tourism became a profitable industry.