i would go to the future get insider information & sports results, look at how i turned out, pick up some cures of disease that we havent figured out yet, go back and enjoy the good life!
I'd go back about 14 billion years and check out the first few minutes following the initial expansion of the big bang singularity.
Or go a few hundred billion years into the future to see what the Hubble constant (or unconstant) and fate of the universe will be.
These choices do present obvious secondary problems, though, like how to avoid being ripped apart/melted/frozen, but hey, that's the fun of make-believe -- you can do whatever you want, lol.