Breakdowns can happen at the most inconvenient times (is there ever a convenient time?) and are sometimes unavoidable; however, there are steps you can take to avoid them or at least limit the consequences. Having your car regularly serviced is, I would have thought, obvious, but do not forget those daily and weekly checks. As a safety net I always used to do every ‘show me, tell me’ check with a pupil as I picked them up for their driving test. That way if something did blow on the way to a driving test the pupil knew it was ok before. It is surprising how many cars are refused on test because of simple faults like bulbs blown and nails in tyres, all of which must have happened on the way to the test centre according to the instructor!
Carry spare bulbs (kits can be bought for each vehicle relatively cheaply), and ensure you have any tools needed to change the bulb as some vehicles have special fixings. Practice changing the bulbs in case it happens to you on test as the examiner will give you a couple of minutes to sort it out. It is impossible to change bulbs quickly on some vehicles, so find out if yours is one of them. Spare fuses are a good idea too; fuses can often be blown when changing a bulb. Disposable gloves to keep your hands clean and some cleaning rags can be useful as well. Never try to cover up information lights on the dashboard, this has been tried before and the examiners are wise to it. If information light is glowing then have it checked out. I heard of one example where the instructor covered the airbag warning light with a postage stamp!
Carry spare bulbs, kits can be bought for each vehicle relatively cheaply.