Being prepared while out on the mountain bike trail is an absolute must and a great rule of thumb is to always pack more mountain biking equipment the farther away from help you plan to be. There are a few important considerations you should also make regardless of the skill level of mountain biking that you plan to partake in.
The first consideration, for anyone planning on being active outdoors regardless of mountain biking or not, should be to have a well stocked first aid kit. You can purchase biker specific first aid kits, that are purposefully designed to fit nicely in a small pack, under the seat or even in saddlebags. A well stocked first aid kit will contain antiseptic, pain reliever, tensor bandages, band-aids, moleskin, and tweezers.
The second necessity is to have a mountain bike specific tool kit and there many options available as to the type of bike you have and the tools you want it to contain. The very basic tool kit should have the required tools needed to repair a flat tire and will fit nicely under your seat or in a saddlebag. Other tools to look for are an Allan key or small wrench, a chain breaker, a tire gauge, a Swiss army knife, and some...