Firstly, there's a difference between "a" shuttle, and "the" shuttle. The Shuttle, as in one of those actually used by NASA, is something that cannot make an unassisted takeoff from anywhere with enough gravity for its wreck to settle - much less fly anywhere afterwards. It doesn't carry enough fuel for that. Now, a generic futuristic "shuttle" might.
Speaking from a layman's standpoint, I think a "shuttle" only really needs an airtight cabin (not even that is a requirement if our spacesuit can connect to an external tank), generators/accumulators to supply power for all the electronics and controls, main thrusters, cold thrusters or equivalent for steering in space, and enough reaction mass (fuel) to get up to speed and stop when it reaches the destination. Heat shielding and rudder/ailerons optional, for atmospheric reentry.
If your shuttle somehow carries enough reaction mass to match velocity with whatever planet it's landing on, it may skip the heat shielding since it'd just be dropping at a reasonable speed, not tearing into air like a meteor.
Now, if the shuttle has "crashed" and is actually repairable, the things I'd expect to have to repair are the hull, the fuel lines, the viewports, the undercarriage, and the computer systems. The thrusters, if they are like modern liquid-fuel rocket thrusters, would likely be terribly hard to repair if damaged, and quite unreliable even if repaired, since they're under significant stress when working. You may have to patch holes in the hull, seal the broken viewports and set up screens with external cameras in their stead (both mercilessly ripped from some unlucky piece of scientific equipment you were carrying, most likely), replace the undercarriage with makeshift sleds, and gut the life support computers to get parts for emergency repairs of the flight control hardware. Remembering to drain and de-gas the fuel lines before welding them, or to close the valves on internal oxygen supply tanks before everything escapes through the holes everywhere, would also be nice.
(note: I don't know how real Shuttles actually operate. I'm speaking with regards to a "fun, semi-simple game")