The question is where do you stop compiling a list of things that might break that you need a spare to replace it with? At least you will I suppose be aiming to get a LHD car so spare parts shouldn't be too much of a problem, there are quite a few suppliers in Europe. I guess the answer is if you see a spare part grab it just in case you need it later. Just see what turns up.
One spare that is worth getting if you see one is a wind-shield, not produced anymore, but make sure it fits the vehicle, van ones are deeper than sedan ones.