When you're out on your mountain bike, the only things you really need to have, apart from a bike suited to the terrain over which you're writing, are a helmet and goggles. Everything else can really be considered accessories, although they're the type of accessories that it also important to have.

But let's consider mountain biking equipment from the ground up.

Bike storage
Where do you keep your bike when you're not riding? If you live in an apartment where space is at a premium, it's always best to hang the bike in a hall, either on the wall or suspended from the ceiling. (Anyone remember seeing that bike hanging from the ceiling in the classic Seinfeld television series?)

If you're fortunate to have a garage, there's plenty of places to store a bike, but since chances are you don't have a kick stand on your mountain bike, the best thing to do is have a bike stand in which to place it. Placing bikes in a stand also simply makes the garage look neater.

Bike tools
Do you want to do your own bike repairs? If so, it'll make it a lot easier on you if you not only have the small tools made for the purpose, but also a large tool - to be exact a truing stand, which will help you true your wheels on occasion.

When you're out on the trail you may have a flat, so of course you'll want to bring a bundle of tools with you. But it's not enough for you to have the tools - you also have to know how to use them. So take some time after purchasing those tools to work with them and familiarize yourself with the methods necessary to fix the various things that can go wrong with your bike.

Bike accessories
What kinds of accessories can you get on your bike? There's such a thing as rear view mirrors, although these are more popular among road cyclists than mountain bikers. The same goes for horns or bells to let people know you're behind them. Also available are bike lights, powerful ones for use when you want to tear down the trail at night.

Bike clothes
Road cyclists normally wear tight fitting cycle shorts and a tight fitting jersey, whereas mountain bike riders do have a tendency to look a bit baggy. The more clothes a mountain biker wears the better, actually, as they can serve to cushion falls. Rather than depending on those clothes, however, you can also stock up on knee, shin, leg, arm, and elbow guards. Gloves are also an essential, as they'll protect the hands from road burn, not to mention increasing the grip on the bike.

Bike security
We live in a world where unattended bikes will quite often disappear. That may not be much of a bother if its only a $20 "beater", but when it's a mountain bike worth hundreds of dollars the loss stings a bit more. Sturdy bike locks are a must.

It's possible to put transponders into bikes so that they can be tracked if they're stolen. Police use this with "bait" bikes. However, various companies are working towards making GPS tracking devices to put on real bikes. They'll probably be on the market in a few years.