Hell, I don’t know… but on the way there I’d be singing:
Fly me to the Moon
Let me swim among the stars…
“Look, I really, really am on the moon. No, I can’t see any stars, it’s the middle of the day! No, this isn’t slowed down film. Look; fine, uneven dust does clump without water. And when I kick it it behaves in a vacuum like nothing on Earth ever could. See; I only have one shadow and it gets infilled by reflected light. This is my camera, see how I operate it with my gloves on. No, it’s not 280 degrees in the shade. See that hill over there? It’s really a mountain bigger than most you’ll see on Earth. And look, it looks remarkably like that one over there. The moon is pretty featureless. Here’s my flag, see how it’s got a crossbar to make it stick out. I really, really am on the moon!”
What is that? It looks like, uh-oh. It’s alive. There is another one. Oh My God! They are everywhere! Dave, look out, they are heading for the lunar lander, close the door before they get in… {static}.
Earhole! (It is safe-for-work.)
Oh God, I can’t breathe!
“Hey, what’s the big idea? This isn’t the Coachella Carrot Festival! I must have taken a wrong turn at Albuquerque.”
“Uh… yeah, so where’s the bar?”
“Ah, shit, I left the camera at home!”
[IZZARD]It’s all sticky![/IZZARD]
I’d sit my happy ass down and then proceed to sing, ‘my bum is on the moon, my bum is on the moon…’
- Get on all fours and do the “dying man in the desert” act, except go:
"Air … air … "
- Make an mp3 of the squealing sound the Monolith made in 2001 on my ipod. Then say something like “what the hell is --” and hit play.
Woo, I’m standing on the moon like a motherf@#*!
You win!
Oh I have another one:
“Oh, hi, Jimi. Hi, Elvis. Who’s that really old guy? Adolf? Really? He’s looking good for his age …”
And since I just mentioned Hitler, I lose. 
" I have to poo!"
or
“What? No Starbucks? Let’s turn this thing around and go home!”
Or
“Hey, I can see Uranus from here!” :::giggle::::
"That’s one small step for man, one giant leap for mankind.
But it didn’t save me a lot of money on car insurance."
I can’t believe I get to do this first! 
I’d start singing!
oh shit oh shit oh shit…
Bwaaaah haa haaa! !! 111!! How the fuck has no-one ever shown me this before. You should get this as a greeting everyday when you access the internet. It should Canada’s national anthem.
As a matter of fact, I do. My boss hates me.
As for my first words, as I stepped out onto the surface, I am of two very , VERY different minds.
I suppose the more poetic would be the third verse of Psalm 148 “Praise Him, sun and moon, praise Him all you shining stars!”.
But more likely I’d be so keyed up that I’d blurt out what Hung Mung said. 
“Hi, Mom!”
Oooh, good one!
I think I might say…
“Somebody pass me the Uranium PU-36 Explosive Space Modulator…”