Obviously, most if not all of our Presidents have held another office before being elected to the Oval Office - just like any good organization, Americans prefer somebody who works their way to the top. And it is true that many of our Presidents have been born in well-to-do families, despite the founding father's desire to break away from the concept of a ruling class. However, many Presidents have some interesting stories to tell in the private sector workforce, before they ever even set foot in a government building.
One big obvious answer is apparent. Of the 43 Presidents we have had up until 2008, 25 have been lawyers. That's a staggering ratio of 58%. Not only that, but every major candidate that we have now running for President in 2008 also holds a law degree, and several of them have practiced law. Obviously, the first thing you should do if you want a shot at the Presidency is obtain a Juris Doctor.
Another career that isn't surprising is soldier; seven of our 43 Presidents served in some capacity of the armed forces before seeking office. Several more have served in the air force of navy - George W. Bush, Sr., was a pilot, and Jimmy Carter was a sailor, both having earned their way up to Navy Lieutenant.
Of all the Presidents, Thomas Jefferson had the longest resume with six careers outside of politics; he had been a writer, inventor, lawyer, architect, farmer. You might be wondering what he invented? The first swivel chair, along with other innovations he put in when he designed his famous home, Monticello.
Contrary to the old chestnut about how actors make great politicians, only Ronald Reagan actually had an acting career before becoming a politician, so one test case isn't very good proof.
Only three Presidents had a previous occupation as writer. One of those being Thomas Jefferson, who almost certainly never got paid directly as a writer, but did his writing in the course of documenting and directing the early childhood of our government. As for Kennedy, his writing was actually helping his father, Joseph P. Kennedy, Sr., complete his memoir of his three years as United States Ambassador to the United Kingdom. As for Jimmy Carter, he has written 23 books, being the only President who qualifies as a professional writer. Granted, all but two of these were written after, and not before, his Presidency.
One other writing career is Benjamin Harrison, who was a journalist by way of having been a court decisions reporter of the Indiana Supreme Court during the time that he was studying law.
While we're on the subject of Jimmy Carter's career, let's clear something up: that title of "peanut farmer" was an exaggeration. He helped out on his parent's peanut farm as a young boy. He shows no evidence of having desired to make a career out of it, and it looks like he gave it up after an accident with some equipment left him with an injured finger.
Harry Truman was the only other President who was also a farmer, although several - particularly the early ones - were owners of plantations. his father was actually the farmer, but Truman worked there for some of his childhood, then went off to finish school and seek his fortune in clerical jobs before returning to the family farm in 1906 and staying on to work there for 11 years, at which point he joined the military. He returned from World War I, married his sweetheart, and opened a haberdashery, making him the only men's clothing retailer on the Presidential list. The farm went bust during the Great Depression.
Andrew Johnson worked briefly as a tailor. He was apprenticed to a tailor at the age of 10, and by age 16 he and his brother ran away to the city, where he found work as a tailor and stayed at it until he'd finished his teen years. Then he entered politics as an alderman.
And, contrary to what you might expect given the poor separation of church and state in the U. S., there has been exactly one member of the clergy to later get elected President - James Garfield, who was a minister and an elder for the Disciples of Christ sect of the Christian Church. He preached his first sermon in Poestenkill, New York.