I wouldn't worry to much but relays on the lights are a good idea. Remember, when was the last time your car was driven all night two nights running. That's over 20hrs of continous use, let alone any bad weather during the day. As regards spares, if it's small and will fit in the boot, take it with you. A spare alternator is a good idea. Petrol injection is well catered for by lots of other entrants. If you are concerned about it now, change it while you have the time and space to do it properly (why are you concerned about these items, are they giving any trouble at the moment ?). You can also take a cue from the spares list for other entrants. Don't spoil your enjoyment of the event by worrying to much about breakdowns ;) It's all part of the fun.