I was not suggesting that I carry things which would be illegal to carry (although I don't think this applies in the UK). it would only be illegal to actually use these things without authority in the UK, not to possess (If I'm wrong please correct me).

Nor would I ever use something that I was not qualified to use. I just wondered if there was anything that would be indespensible to have available in the event that someone qualified to use it was there but off duty and had no equipment with them.

The oxygen is an idea but there is no way I'm going to lug a cylinder around with me. same with back boards. This is for EDC in a daypack not a vehicle.