If you had to tile the universe with something - something simple - what would you tile it with?

Copies of my genome. If I can't do anything to affect the utility function I really care about, then I might as well optimize the one evolution tried to make me care about instead.

(Note that I interpret 'simple' as excluding copies of my mind, simulations of interesting universes, and messages intended for other universes that simulate this one to read, any of which would be preferable to anything simple.)