There is no quicker way to ruin a good ride than to get a flat. These are some of the items you should carry in your pack to get you back to riding as soon as possible and save you from a long walk back to your car. You don’t need everything on this list, but you don’t want to ride without the essential items highlighted.

helmet (save your head)
spare tube (easier and quicker than patching)
pump or CO2 dispenser with cartridges (you need air to ride)
water hydration pack or water bottle (hydrate or die)
tire levers (needed to ply a tire off your rim to change tube or fix a flat)
first aid kit (to stop the bleeding in those bad crashes)
patch repair kit
allen wrench tool (bike adjustments to seat, bars, etc.)
sunglasses (blocks wind, sun, and bugs)
mp3 player (crank it up)
toilet paper (softer than leaves if you gotta go)
suspension pump (for full suspension riders)
cell phone (in case of emergency, or to find your trail buddies)
first aid kit (to stop the bleeding in those bad crashes)
pocket knife (just in case you need to defend yourself against wild animals)
tweezers (good for picking the thorns out of your tires and your skin)
chain tool (fix a broken chain)
mosquito spray (keep those nasty bugs off you)
camera (for capturing those Kodak moments)
energy bars or gel (fuel for the body)