Everything that can come off your bike probably will at some point: derailleurs, cranks, pedals, head set, even your handlebars.

• Although proper bike maintenance and handling will minimise the likelihood of things loosening and falling off, you’ll probably find yourself in a pickle at some point. Especially if you own an ageing bike that you bought second-hand. 
• So spend money on a multitool that you find easy to use and which, ideally, sits flat in your pocket. One of our TWC writers carries a multitool AND her most-used Allen key in a full size because she’s weak and doesn’t trust herself to fully tighten things without the extra leverage.