1. MTBing bell to warn upcoming hikers or bikers of your speedy downhill run
2. Appropriate pedals for your ride
3. Multi tool to tighten the screw you never t thought will come loose during your ride
4. CO2 and pump regulator when you need lots of oil quickly
5. Never hurts to have an extra inner tube in your backpack just in case nothing else works and you don't want to walk 10 KMs back to your car.