I own and operate a dump truck. I haul things like rock, dirt, sand, etc, and I buy all of the material that I haul. what expense category do I list those under?

[LeonardS]

If you use Schedule C to report your income and expenses you could enter these items as supplies on Line 22.  If you want a more detailed listing you could list them individually by type in Part 5 Other Expenses.

[Carl]

I buy all of the material that I haul.

If you sell that material for a price more than you paid for it, then it's inventory. However, you also have the option to treat it as a supply expense. I myself would treat it as a supply expense since we're talking about raw earth materials, when you get down to brass tacks.