Complete set of bulbs, hi vsi jacket for EVERY person in the car, triangle, fuel in a METAL container, E111, minimum amount of CASH when travelling through germany as they have vagrancy laws, headlight convertors, if not a EU plate symbol plate then a GB sticker, insurance cert and license would be a wise move, and also V5, as well.
Just be aware speed limits are a lot more enforced over there, radar detectors will get you arrested if you plant to come back through france.
If you were doing spain a bail bond would be essential as well.
There's probably more so I would search on AA RAC websites, as each country different.
tabetha