I do martial arts on a heavy bag. Meaning punching and kicking the ish out of the bag. Great cardio and total body strengthening including your core.
And therein lies the most important part of your body to work out... the core. Your core is crucial for better balance and overall strength. I didn't realize how important it was to my riding until I worked on it all summer in prep for winter.
Last season, I was almost 30lb overweight and just plain out of breath from the stupidest activities. I bought a heavy bag and hit it up at least 3 times a week sometimes for 2 hour sessions.
My wife also bought this thing called the "Ab Wheel." I initially laughed it off until I tried it. Holy cow was it hard to do. I mean I could only roll out part-way about three times on my first try and the next day my abs felt shredded. I kept it up and now I can do over 20 a day without getting super soreness.
Fast-forward to this season of riding and I noticed a HUGE difference in my riding. I feel way more stable and am able to manipulate my board better. I also noticed that I'm able to power out of a lot of mistakes that just last season would have caused me to bite it.
Ab wheel... such a simple affordable tool to add to your routine.