Works of art that require thousands of lifetimes to complete. Deep understanding of the physical world. Exploring the universe. Much more.
Re: creating new beings. How long till you also get bored of that? Remember we're talking about quadrillions of years.
An additional thing to consider: if you could live quadrillions of years and still be able to perceive things that take thousands or millions of years to unfold, wouldn't you subjectively be living the lifespan of a normal human being? That is, your life wouldn't feel long to your mind, but normal (your mind would have to adjust to run more slowly). Wouldn't then regret your "short" lifespan and wish you could live longer?