In Dec we took my wife's 89 300CE to Vegas. Kept the car between 80 and 100 on stretches across Death Valley and the Majave Desert. All I took was a radiator, my cell phone, and the AAA 100 mile towing card. Seriously if I were doing the traveling you are going to do, I would check or replace the belt pulleys, and if the radiator is tired, I'd replace it too. As for spare parts I'd take an OVP, EZL, and one fuel pump. You can bypass the fuel pump relay with a jumper, and the car will run fine without the computer. Mileage and performance may suffer a little, and warm up will be rough, but the car will run fine with the ECU disconnected.
Good luck,
Peter

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