The AA has a good website with solid advice about driving in Europe
European Driving : European driving advice from the AA - The AA
I would have thought that as long as you carry the original registration, MOT, insurance and driving licence you can't go far wrong.
Also, some countries require you to carry a reflective vest.
Check on whether the countries will allow you to have speed camera warning devices (if you have one).
Take lots of euros in case you credit cards don't work at automatic filling stations.
Michelin maps, the yellow ones, are great - look for the 'green' scenic roads
spare bulbs, tool kit, breakdown cover, change direction of headlight.
Someone else will along to offer much better advice than me