Any question answered...

OK, what's the best bicycle tool out there to carry with you for emergencies. You know the multi-tool type thing but which one and why?

You might be approaching the question in the wrong way.

• Why do you think you need a multitool?
  
• The times when you've needed tools, what broke and what did you end up needing to fix the problem?
  
• How often are you out of range/hours of a bike/hardware shop?
  
  

Personally I only ever make sure I have something if I'm on my road bike. Then I just have one of the cheap park ones (allen keys and screwdrivers) plus tyre leavers, tube, gas canisters. If it's just going around london, then I think anything that breaks will either be fatal, or can be ridden away carefully, or I'll walk to a shop.

Failing all, you can take a cab, which will probably be under £20... which is probably about what you'll spend on an 'emergency' tool you don't use.

If it's for an mtb, then I recon a quick google search for mtb forums will probably give you a better answer.