You will often see lists of things that you can do with your commercial pilot certificate either as a job or to build time for the airlines. You can work for a Part 135 operation or in a corporate flight department operating under Part 91 but there are other things you can do as well. You can even fly individuals in their own airplane for hire. You can’t carry them in your airplane, since this would be a Part 135 operation.
§119.1 of the FARs is where those other activities are spelled out—basically listing exceptions to needing to comply with the rules for air carriers and cargo operations.
(e) Except for operations when common carriage is not involved conducted with airplanes having a passenger-seat configuration of 20 seats or more, excluding any required crewmember seat, or a payload capacity of 6,000 pounds or more, this part does not apply to—
(1) Student instruction;
(2) Nonstop Commercial Air Tours conducted after September 11, 2007, in an airplane or helicopter having a standard airworthiness certificate and passenger-seat configuration of 30 seats or fewer and a maximum payload capacity of 7,500 pounds or less that begin and end at the same airport, and are conducted within a 25-statute mile radius of that airport, in compliance with the Letter of Authorization issued under §91.147 of this chapter. For nonstop Commercial Air Tours conducted in accordance with part 136, subpart B of this chapter, National Parks Air Tour Management, the requirements of part 119 of this chapter apply unless excepted in §136.37(g)(2). For Nonstop Commercial Air Tours conducted in the vicinity of the Grand Canyon National Park, Arizona, the requirements of SFAR 50-2, part 93, subpart U, and part 119 of this chapter, as applicable, apply.
(3) Ferry or training flights;
(4) Aerial work operations, including—
(i) Crop dusting, seeding, spraying, and bird chasing;
(ii) Banner towing;
(iii) Aerial photography or survey;
(iv) Fire fighting;
(v) Helicopter operations in construction or repair work (but it does apply to transportation to and from the site of operations); and
(vi) Powerline or pipeline patrol;
(5) Sightseeing flights conducted in hot air balloons;
(6) Nonstop flights conducted within a 25-statute-mile radius of the airport of takeoff carrying persons or objects for the purpose of conducting intentional parachute operations.
(7) Helicopter flights conducted within a 25 statute mile radius of the airport of takeoff if— [Lots of stuff about limitations here]
(8) Operations conducted under part 133 of this chapter or 375 of this title;
(9) Emergency mail service conducted under 49 U.S.C. 41906;
(10) Operations conducted under the provisions of §91.321 of this chapter; or
(11) Small UAS operations conducted under part 107 of this chapter.