If you are riding some trail on your mountain bike, then it is not a matter of if something will break, it is when. To be prepared for it is wise.

The image shows the tools I have in my toolbox for my daily rides. Starting clockwise from the left is my multi-tool. It comes with the normal tools but it also includes a chain tool to detach and replace broken links.

Next is the pump. It is a double action pump that inflates on both strokes and it saves a lot of time inflating mountain bike tires. Another option is to ride with a CO₂ cartridge.

You need two of these tools to remove the tire when you get a flat, but you could get away with only one. Next to it I have my roll of electrical tape. It has no specific use but I have used it for all kinds of emergencies, like attaching a racing number when the zip ties broke.

A spare tube is great for the first flat and gets you back on the trail in no time. Be careful not to pinch the tube when you put the tire back on the rim. 

The "missing links" are just great to fix a broken chain. You remove the broken link in your chain and replace it with the missing link, snap the outside on and you're good to go.

For the case where you have more than one flat and you've already used your spare tube, a repair kit with glue, sandpaper and patches are a must. Some of the regular flats we get are cased by pinches when the something like a rock pinches the tube between the tire and the rim. For most of these you would need two patches. The last ride we did at NorthStar left us with 6 pinch flats, requiring 12 patches. This is where the electric type is a great emergency fix to get to a place to get more patches or tubes.

After one of our last team rides I am going to add one more item to my list of "must haves": Zip ties. On this ride one of the ride leaders' shifter mount broke where it was mounted on the handle bar. If we had some zip ties, we would have been able to fix the bike right there.