If it is a manual, chock the wheels do not use the emergency brake. Gas should be fine for 3 months. Use a trickle charger if you can, or disconnect the battery completely. Try and put it up dry, if it is wet try and get a hairdryer to the brake rotors and pads to make sure they are dry. Some sort of de-humidifier is a bonus, also put the windows down a fraction if it is inside.

I have left cars longer periods (over 6 months) with few problems. Main problems have been the brakes getting stucking on (which also came free with enough gas, but I buggered the rotors a couple of times). Condensation in the car making it thoroughly horrible and needing a good clean. I never had a problem with fuel and always disconnected the battery.

__________________
2003 X5 3.0i Manual