Joe made most of his money in the stock market. He traded stocks in the roaring 20s when there was little regulation and "anything goes" attitude surrounding all of Wall Street.
Joe famously avoided the Great Depression, and stock market crash of 1929. He sold his entire portfolio days before the crash. But how did he do it? This one anecdatoe explains it all:
"Joe Kennedy exited the stock market in timely fashion after a shoeshine boy gave him some stock tips. He figured that when the shoeshine boys have tips, the market is too popular for its own good.
A theory also advanced by Bernard Baruch, another vested interest who described the scene before the big Crash: "Taxi drivers told you what to buy. The shoeshine boy could give you a summary of the day's financial news as he worked with rag and polish. An old beggar who regularly patrolled the street in front of my office now gave me tips and, I suppose, spent the money I and others gave him in the market. My cook had a brokerage account and followed the ticker closely. Her paper profits were quickly blown away in the gale of 1929." - Fortune Magazine, When Shoeshine Boys Talk Stocks