Many jobs require items that can only be obtained by purchasing them. You can see icons of the required items in the job lists.
You can purchase them in the inventory section for the appropriate city.
You can also invest money in land and buildings (New York) and businesses (Cuba and Moscow) and corrupt politicians (Cuba).
Some long-time game users have rackets instead of real estate in New York. Though you can no longer get rackets, some players still have the game version with them. They cannot get real estate in NY.
While avoiding spoilers, it is worth mentioning that a large portion of income goes for bribery costs in some cities. It is arguably to your advantage to start developing your businesses in a new city the minute you have access to it.