From Kent Brown, Senior Vice President & Transportation Practice Leader, Hylant:

There are certain coverages that are absolutely essential and required by law. Those include:

1. Auto liability. Make sure in your auto liability program that you have coverages that are very specific to your industry.
2. Cargo. This covers the vehicles you haul and includes constructive total loss and diminished value.
3. General liability. This provides coverage for liability claims not involving your trucks. It is not a very expensive coverage and is typically required by your shippers.

Beyond those three, it comes down to individual preference and condition. Read more about recommended coverages.