Keychain style flashlight or headlamp, LED type, not incandescent: The keychain style is tiny and lightweight, the headlamp style is a bit bulkier but easier to use. You can get these for a couple of bucks or less at the local big box hardware store. The LED ones are lighter, more durable and last considerably longer. Very useful if you need to make a repair after dark! I keep a keychain style one as a backup as I normally have a headlamp in my backpack.
It includes nine tools: seven hex bolts, one torx bolt (the star-shaped one), and a Phillips screwdriver (also the star-shaped one). Like Peter says in our guide, if you have a newer mountain bike or road bike it pays to take a quick look at what types of tools you need, as torx bolts are becoming more common. And a quick glance at the bottom of your shoes or derailleur bolts will confirm if a Phillips head is the right choice.
Friction gear systems are a lot simpler to adjust, because the movement of the derailer cable can be modulated as you ride, every time you change the gear- they require less cycle maintenance. Modern index shifting systems are a little more complicated because each ‘click’ must release the exact right amount of cable to allow the derailer to move the correct distance to move the chain from one gear to another. Setting up and adjusting a derailer is not difficult and requires only basic tools, but there is a methodical procedure to follow.