Take as many spare parts as possible. Try to think of all the parts that can fail on a long journey like that.
I would take things like fan belt, fuel pump, condenser, set of points, wheel bearings, drive shaft couplings, complete set of engine gaskets, some spare oil, just the most obvious things that pop in mind. As long as you have some tools you should be fine. And in the worst case scenario, you still have the van.
Also make sure you got some suitable ramps to load the car and of course some straps. Lets hope the 126 will only be in the back of the van during the ferry crossing.