One thing I did that was a blast is start a new island seed where I could build on the island I spawned on. Because I had already squeezed everything out of the game on my original seed without mods or admin, I just used free build to build out a cool base without exploring off the island. When the game is finished, I have an awesome base and an untainted world to conquer. Of course, I kept my "main" world for normal play. Great way to have a blast while waiting for the game to be finished!