W/C & Gen Lia Insurance.
Vehicle insurance, usually at MUCH higher levels than your state minimum.
I also have to have a HUGE umbrella policy & I came out of retirement and have no employees or crews.
They also will not take an individual anymore around here, so you must be a legal business entity.
I'm a C-corp, but they will take LLC, S-corp, legal partnerships etc etc.
Then of course you must have all your own everything & spares.
I have 3 bucket trucks, a bunch of meters, 100+ coring tools, dozen drills, etc etc from when I was an actually a bigger contractor.
The point is you can't call up and say my truck broke, my meter got ate by the dog etc etc.
That's if you can find a guy willing to take you.
Some projects will not take just a guy, they want bodies.
Good luck,