There are big Camelbaks and little ones. Once you decide you like mountain biking, it's time to buy a backpack -- maybe a big one and a little one.
You've seen riders with those little backpacks, called "Camelbaks" by most of us because that's
the most popular brand. This is the gold standard of "taking it with you." It holds water,
lunch, emergency supplies and just-in-case clothing, tool kit, car keys, everything.
The disadvantage of an underseat pack? No matter how tightly you lock it on, eventually the straps will tear loose. I fix mine with strips of water-jug plastic to reinforce the case, shoe goo between the layers, and rivets.
There are other options. I like an under-seat pack for my basic toolkit. It holds multi-tool,
quick-link for the chain, spare tube, patch kit, a couple of CO2 inflators, plastic rain slicker,
and single-use mosquito repellant and sunscreen pads. So it's always with me, even if it's
a 15-minute jaunt -- without backpack -- from my front door.
For rides up to 2 hours, I only take a backpack if I'm doing video. I love the freedom of a bottle in the back pocket.
Some riders, racers in particular, keep everything in their jersey pockets. Water bottle in
the cage on the frame and another in the back pocket and you're good for 20 miles. Bike tools
on one side, spare tube and patch kit on the other. (I like to have my mini-pump attached to
the bike frame, but you can stash it in a pocket too.)
With two 24-ounce bottles, you're set for a substantial ride. But for hot, long, hard days in the saddle, you really need the increased water capacity of a backpack!
Some riders like lumbar packs aka "fanny packs" because they get the weight off your back.
So it's a bit cooler, and you can move around on the bike more easily, with less backache on
long rides. You won't see a lot of these on the trail, but they actually work very well for
intermediate-length rides.
