flyfish,
The skills test includes your ability to plan X-Country flights. Presumably your instructor has already taught you how to handles stalls, emergency situations, etc?
The X-Country solo is more of a confidence builder than anything else. All planning, etc, should be checked by the instructor before you set off on what is actually a supervised solo flight.
Remember, the checkride (skills test)is merely a second opinion to verify the instructor has done his/her job.