I started out hauling 700 gallons of JetA and xxx gallons of pesticides with a 1-ton pickup and 35' goose-neck trailer when running ground-crew for a cropduster. Surprisingly enough, the part that required me to get a CDL was the fact that our water tank on the trailer was over 1,000 gallons, so I needed a tanker-endorsed CDL. I ended up getting the HazMat while I was at it, because there was a chance that we would carry insecticides in reportable quantities.
It was like pulling teeth trying to explain to the DMV folks that I only needed a Class 'C' (because it was a pickup truck) but still needed a tanker. They went as far as to pull out a book with pictures of the different combinations of vehicles - semi pulling dry trailer, semi pulling tanker, pickup pulling dry trailer, etc. They pointed at the semi and said "See, you need a Class A!". I pointed at the drawing of a pickup pulling a water trailer at the bottom of the page and said "NO! See, I need a class C!". The lady slammed the book and went back into her office. Luckily, the desk jockey that I dealt with was not the one that gave me my driving test (which I took in my personal pickup).
After the cropduster job, I went to running ground application equipment. For that job, our 'nurse' rigs were semi's, so I had to 'upgrade' to a Class A.
After that job, I worked part-time as a bus driver for the city transit system, so I ended up with Class B w/ pax endorsement.
At one point, I had my PP-ASEL-IA + medical, CDL-ABC-Tanker/HazMat + medical, and Commercial Applicator's License (pesticides) with Insecticide, Herbicide, and Fungicide endorsements. I didn't have room in my wallet for money because of all the paper/plastic endorsements I had to keep handy (?luckily? there wasn't much money to keep in there in the first place).
When I got my GA driver's license last year, I kept the Class A/B w/ Tanker, but let the HazMat lapse. You never know when someone will need a load of beer hauled across the country in 2 days...