Originally Posted by mlh122

I don't usually upgrade stuff that works fine. If something breaks or you realize its lack in quality is affecting your ride, then upgrade it to whatever you see fit. As far as things you need:

helmet, maybe body pads too, that's personal preference
small toolkit/flat kit (multitool, spare tube or 2, strong tire levers, frame pump and/or co2 pump)
first aid kit - a $6 one at a supermarket should be fine
gloves - padded or not, they prevent blisters and calluses, and can make a wreck easier on the hands.
sunglasses - keeps rocks/bugs out of your eyes, and can make a bright sunny day easier on the eyes
water bottle or camelbak - since im too lazy to wash my water bottles, i just use bottled waters bought on the way to the trail. my wife has a camelbak and loves it
ankle strap - if you ride in long pants these keep them out of your chainring. i use them a lot in cold weather riding. i usually lose them over the summer, but they only cost like $2
map - if the trail is long or remote a map is a very good idea
compass - same reason as map
gps - basically the same as map, but a fun toy.
cell phone - i carry mine all the time no matter where i'm riding, and keep it on in case i get lost or injured rescue teams can track it.
sweat wicking shirt - good for most people, but an absolute must for sweaty fatties like myself.
food - a small snack is great on a long ride. power bars, trail mix, nuts, an apple, whatever
heart rate monitor- not a necessity but good if you're trying to lose weight, they have an alarm for if your heart rate gets too high too.
notification - tell someone roughly where you're going and when you expect to be back. i usually leave a voicemail with a friend or family member or 2. that way if i don't come back they know where to start looking
friends - its safer to bring a friend rather than ride alone, not a necessity though, i usually ride alone.
biking shorts - lycra or baggy - may or may not be a necessity, depending on who you ask
lights - in case you get lost and nightfall comes, it's easier to find your way back if you have a light.
change of clothes - in case of blood, water, mud that you don't want to get in the car. also in case you're way out in the boonies and the car doesn't start, you can put warmer clothes on and stay the night or try and ride towards town till you get cell reception.
sunscreen - depending on how easily you burn and how long you'll be out. i usually don't wear sunscreen if im biking in dense woods, it will just make bugs stick to you better.

that's all i can think of for now.