#1.
One of the most important parts on your bike that are sometimes overlooked are your brakes.
Having working front and rear brakes is definitely something to check before you put your gear on and hit the trails.
Without the certainty of being able to stop on a dime, you will see yourself (and your bike) fly off the beaten path and do cartwheels through the air!! Mountain bikes are now equipped with disc brakes and when working right, they are very responsive.
The great advantage about having disc brakes on your bike versus the type that would slow your wheel down on the rim of your wheel is that there wouldn't be any mud, sand, dirt or even snow that could get stuck into the braking surface and therefore preventing you from slowing down.
I check the brakes on my bike before every ride so that I can be certain that I will be able to stop or slow down when needed.
I also spin each wheel and check and sometimes double check that each disc isn't coming in contact with the braking surface.
Be sure to keep a close eye on your brakes and if you notice the slightest problem, be sure to get your brakes fixed or replaced so that you don't end up doing cartwheels off the edge of a mountain!! #2.
There are many clothing options that a mountain biker can wear and one of them is mountain bike gloves.
Unlike cycling gloves where you can see your fingers, these gloves cover your entire hand and right up to your finger tips.
To make this brief and to the point, I'll mention a couple of benefits of wearing mountain bike gloves while riding.
If you crash, (hopefully you don't!) this type of clothing will protect your hands as you could fall onto a jagged rock, sticks, mud or anything else that could be harmful.
Also, you will have a much better grip when riding in the rain or if mud should happen to get on your handlebars.
There are many more benefits to wearing mountain bike gloves but these are the most noticeable values that I've seen when I'm out mountain biking.