On Dr. Evil's spacesuits in Austin Powers: The Spy Who Shagged Me we can see a list of chemicals. The first two are obviously water and oxygen. But the final one, P^2 is not the notation for any chemical that I know of. "Pee squared" doesn't sound like something that I'd want in a spacesuit. Is it some sort of isotope? Or is it a joke or mistake?
Considering the rather lowbrow humour of the Austin Powers franchise, I'd say this is almost certainly a "pee" joke. As a matter of fact, real-life astronauts wear special diapers under their spacesuits, so they can go to the bathroom without soiling them or having to take them off.
As a side-note, P2 is the chemical formula for diphosphorus, but I doubt that's the reference here (note the subscript '2', as opposed to the superscript '2' on their suits).