Agree with Wohlmeyer!
Adding a few ideas taken from multiple road trips in my other classic car (a '72 Pontiac)--albeit my trips were only six-hundred miles round trip (so half yours). I always like to tuck away a gallon of distilled water, a quart or two of oil, and my AAA membership card. If you don't feel like sticking a gallon container of distilled in the boot, transfer the distilled water to a several "spring water" bottles you keep on the passenger floor up front. Their small size helps you pour them into the header tank with little "glug-glug-glug"-ing of a coolant bottle, and you can drink them in a "thirst emergency".
Before you go, I'd go online and purchase an AAA service with the maximum allowable mile towing allowance (and gasoline allowance; up to five gallons premium, if you specify premium when you call). It sure would suck to have to get your car towed six-hundred miles, at two to three dollars a mile (which will not happen, mind you; but better caution rather than anything else). And be sure to write down the towing points for the car--if you should for some unfathomable reason break down, it's usually best to ensure your car isn't damaged by the responding party. Obviously, you already know the way to haul the car onto a flatbed, but...sometimes details like this escape us when we're frustrated and angry from a breakdown. Thus, illustration to the rescue.
Oh, and of course the obvious, which is to check your tire pressure and tread depth before you head out. If your tread is below the depth you deem "safe to be caught in torrential downpour doing 70+ on the interstate", you should be fine. I would never go on a road trip with less than 4/32nd's on my tread depth, but that's just me.
Also, you might wish to get "WAZE" app on your cellular device for traffic updates posted by fellow travelers.
Furthermore, you might want to make sure your AC is running well. Took a trip to Florida way back in 2006 in a 308 GTS whose AC was not exactly blowing super cold...even with the top off the car, it sure was a scorcher in that cabin.
That's all I can think of--most importantly, the list of Lotus Ltd. members is a great way to ensure peace of mind, and is probably far more important than the previous little "so incredibly obvious we sometimes forget" tidbits.