Whatever critical items you have, if you plan to bring spares of them, might as well install the good (new) ones into your car, and keep the old "okay" parts as spares instead.

What's the condition of the radiator? What's the condition of the brake rotors? These items don't typically require spares, but if they're questionable, might as well replace with new.

If you'll bring a spare set of engine mounts, don't forget the transmission mount too. Are the flex discs in good order?

Agreed on getting the oil pan skid plate!!

Don't forget the usual emergency items like a shovel, tow rope, flares, a durable jack, a spare w/ new or good (and inflated) tires, and some tire repair kits (in case of a puncture). Make sure the battery is good and that you also carry an air compressor.