For me the bicycle has been everything (and diet). I grew up as a fat kid, which was mainly from my parents feeding me shit over time. I eventually got sick of it and created my own weight loss regiment when I was about 13. Didn't follow any anti-carbo-glutan whatever bullshit, I simply ate healthy things and in moderate amounts. Completely cut out fast food and highly-processed foods, as well as soft drinks and other sources of concentrated sugar.
For exercise, I had a mountain bike and would ride around 10 miles about 4-5 times a week. I loved biking so this was a really good way to stay focused and have fun losing weight, rather than hating the exercise and giving up. The problem with most exercise routines is that they are fucking boring and people give up due to lack of interest (why I don't always think these weight routines are the best thing). I did do a little bit of upper-body resistance training with a Bowflex, but nothing very serious. Following this I managed to drop 40lbs in about 4 months, which is a lot for a young kid.
Since I lost that weight, I haven't changed my diet or exercise habits at all. One of the biggest misconceptions people have is that once they lose the weight, they can go back to being a gluttonous sloth. unsurprisingly, they gain all the weight right back and get depressed. In order to keep a healthy fit body you have to lead a healthy fit lifestyle - you really can't let up on it.
Today I'm in the best shape I've ever been in, which is mostly from a combination of cycling, hiking and doing physical work. I generally hate working out, and rarely do it. Cycling is fantastic because it builds up a super strong heart, you get huge powerful legs and it even builds a good core because your stomach muscled are tensed when you're riding. You will not look like muscle-head Joe but you will be cut and lean.
Being lighter is huge for snowboarding. I think back to when I was overweight and how much harder of a time I had controlling and throwing the board. Being agile and lightweight improves your riding so much, and also makes you more resistant to injury.
PowderHound and TreeNinja