Make sure your seat height is correct. Too low could be part of the issue with the leg pain.

Carry with you - spare tube, patch kit, pump, tire levers, multi tool. For longer rides consider having something to use for a tire boot (in case you slash your tire). Money. Cell phone if you want, if you're far from home/car. Chain tool and spare chain pin if you start going farther from home/car also.

Do not use slime in your tires. It doesnt' work well, and will prevent patches from adhering if you try to patch.

If you're riding on knobby tires, consider something like this: http://www.biketiresdirect.com/produ...ntry-rock-tire . It's slick enough to roll fast on the street, but still has some tread for dirt. I have these on my kids' bikes and like them a lot.

Get your wheels checked after a few hundred miles to make sure the spoke tension is good.