It's a jumble of evocative ideas that make sense to somebody brought up in the U.S. (and someone the right age). King is drawing an analogy between the insurance policy and various gambling games or situations. In this case, the dark humor is that you win the game (collect on the policy) if someone dies. "Seven-come-eleven" is another name for a dice game commonly called "craps." So it is a reference to chance. "Die the secret death and win a hundred dollars" is likely a reference to a radio and TV quiz show of the 1940s, 50s, and 60s, usually called "The Groucho Marx show" (the official title was "You Bet Your Life"). The main entertainment was Groucho Marx interviewing contestants and cracking jokes. There was a "secret word," shown to the audience before the show. The announcer would say, "Say the secret word and divide a hundred dollars. It's a common word, something you say every day." The "secret word" might be something like "elephant." If, while being interviewed, the contestant happened to say "elephant," they would win a hundred dollars.