Importing hazardous waste.

Then probably food, clothes, meat.

A college town is also really important at the beginning. Research has changed the game a lot.

Oil is a good choice because it works without workers and is high enough value per ton to not overload the truck side of the customs house.

Unfortunately, in the newest versions, you have to first research some geology thing in the university first, before the mini map will show you where the resources are. You can still try to find the stuff manually, though.

Raw Bauxite is another option for similar reasons, but the resource is rarer and I think the raw stuff is less valuable than oil.

Once I do have my own workers, clothes are an obvious next choice. That industry is fairly cheap and easy to set up and the price difference between fabric and clothes makes it super valuable. It also allows for an easy next step by producing your own fabric as well.

Once I have some money coming in, I like to build a gravel industry. Not even for export, just because the stuff tends to clog up the border if I import it.

I don’t like to build farms early on. The capital outlay is too high, the value gained too low, and exporting crops with trucks is a big no no

Mid term, I always try to go towards a steel mill. The capital outlay for a (well-working) steel mill is extreme, so don’t try to start this before you have some good income, but once I have that thing working, I find my money problems will just go away after two or three years.

Definitely oil, you don’t even need the refinery to start earning.