I would add something useful like say... A portal that takes you any where, but you don't know where*
I would reverse the economy making ores and diamonds and stuff cheap while making wood cobble and stone and stuff expensive!!!!
That's so useful that I can't even wait for it to be released I would encourage guilds, teams, groups and big projects that move the economy and take the boring out of minecraft
Well, knowing me, I would start out as a good and just ruler, then slowly succumb to the absolute power that I would possess. I would gradually become more and more corrupt and evil until I eventually enslave all of EMC to spend eternity mining gold and lapis from my mines.