Ice Rocks
Elon was chill enough without this, but finding and analyzing ice, even under the surface rocks, would be a significant step. The popular press focuses on the use of ice for moon colonies but it will also provide scientific researchers with ice samples to compare with measurements we have made of particular comets, asteroids, and meteorites as they delve into the history of the Earth and the solar system.
I can't offer the boffins a pint (beer should never be colder than cellar temperature, regardless of what my fellow Americans think, so I'll substitute a gin and tonic.