The USA does not have nomads.
When you file taxes, you pick full year resident, partial year resident, non-resident.
If you select non-resident, you will be a resident of another state at the same time.
In your situation, don't you have a permanent address somewhere?
Where does the DMV, IRS, and other agencies/companies that always send hardcopy paperwork to you? That is your address and that is where you would get your health insurance.
So it that's not in California, make sure you are purchasing a plan that allows full out of state coverage.
In response to the comments:
Of course, you paid US and CA taxes last year.
If you earn money in CA regardless if you are a resident or not, you owe taxes on this money.
If you filed these taxes as a "resident" of California, then you are a resident of California and you are breaking the law having a NY license and car insurance.
If you filed taxes as a "non resident" where did you file your residency taxes.