Every book you’ve ever read is a different combination of 26 letters.
More impressively, DNA is made up of 4 letters. These four letters (A, G, C, T) make up everything that has ever lived, everything that is currently living, and everything that ever will live.
Even more impressively, everything in the universe, including the aforementioned DNA (with the exception of dark matter, of course) is made up of three things: up quarks, down quarks, and electrons. This includes all of humankind, the Earth, the sun, Mars, and probably the entire universe.