If I had my original body back, the first thing I would do is...

Screw Winry. And Riza and Sheska and Rose and Teacher and Maria and...

Eat Mrs. Hughes' apple pie, along with a crapload of other edible things.

Drink milk. Just to piss off Ed.

Take a long, relaxing, hot bubble bath and then shave my five'o'clock shadow, which I'm sure is quite prominent by now.

Sleep.

Compare measurements with Ed. And I don't just mean height.

Do the Macarena.

Become the main (taller and handsomer) protagonist.

Replace the loincloth with designer jeans.

Take a shit on Mustang's desk. I wonder why Ed didn't do that a long time ago.

Find Nemo.

Catch Kira. Wait, what?

Become Fuhrer.

Kill the Uchiha clan.

Bake lemon cookies.