What jobs can generate income whilst on a road-trip across northern USA?

Sorry, but you are just going to have to save up enough money to support yourself on your visit to America. It is absolutely illegal to work while in the U.S. on a tourist visa or under the visa waiver program. That car bit is simply not true. Very seldom a person needs a car delivered to another part of the country...and pays a bonded service or person to do that...no way is anyone going to just let a stranger drive their car ...and you certainly could not legally sell it. Absolutely NOBODY buys encyclopedias from door to door salesman, in the age of computer based encyclopedias. Unemployment is increasing in the U.S. right now, jobs are going to be harder and harder to find..and besides, you cannot work when here as a tourist.