Wheel Nut:
FWIW a 17 year old girl has to open the car bonnet and show the examiner how to dip the oil on test
and lots of other things… more added as of 1st July.
http://www.fancyacar.co.uk/learners/show-me-tell-me-questions-for-driving-test/
I’d try my best to never be stuck for a bulb on the road. Carry a few in my bag. As has been said, bought by the box from Auto Electricians or Motor Factors (NOT Halthieves) they’re only pence a piece.
If completely stuck one can often be “borrowed” on a temporary basis from elsewhere. i.e. Indicator or brake light bulb (21 watt) from reverse or fog light. Just watch they have the same number of pins. (contacts) 1 or 2.
A tail light bulb (5 or 6 watt) from the number plate light (nobody’s going to throw the book at you for running without that), or unit storage locker light, or even one of 2 or 3 per side from the unit’s rear lights. Again, watch the pin numbers, they do have a habit of being 2 pin on trailers and single on units.
If you’ve got multiple bulbs in the tail lights, usually at least 2, often 3 you should never be completely in the dark whilst out on the road even if 1 bulb blows.
Another, get out of jail trick… you can use one of those tail light bulbs as an indicator bulb. Not so good to see in bright sunlight, but ok otherwise. MIght flash fast & put a fault warning up on the dash, but at least you’ve got an indicator.
We carry boxes & boxes of bulbs in most of the units as we have to completely strip the trailer rear lights down for unaccompanied shipping to prevent theft. Some of the older trailers were on single pin, a few on square lenses (against the majority of round) so we had a right mixed bag of gear. (not forgetting the palm coupling adaptors aswell!) Hence easy to accumulate a few bulbs & lenses of my own 
In daylight at least, i found out 1 day, you can even get away with round lenses in square rubbers
(would show white light at night).
If you’re stuck for basic tools, remember owner drivers usually have them. (might take a lot of polite begging though). Or i’d buy them on the road and claim it back. I’m sure they’d rather reimburse a £2 screw driver than pay a £100 call out bill.