New DME relay
New fan belt (and the right tools to change it)
Fresh wiper blades.
One new plug top cap
1 litre of engine oil
tyre pressure gauge
One new can of puncture repair (the inflating type)
Bulb kit
Any thing needed legally in the countries you are passing through, read the excellent RAC guide on their web pages.
RAC insurance cover for break down
Do a Pretend MoT on the car for wheel bearing wear etc
Ensure wheels are balanced for 80 mph!
Oil change
New petrol and air filters
Check the jack works
Small tool box with spanners, pliers, screwdrivers etc.
Check the places you are visiting for Clean Air regulations and a sticker for your car.
If using French autoroutes/toll get a remote sensing device (they are cheap) that allows toll gate passage without getting out of the car or finding the cash.
Good large scale maps.
Sure there are more things, but the above has been my prep over the years.
