Well the number one thing that can really help your riding is probably skateboarding. Pushing it hard skateboarding you get a serious workout as well as you get used to alot of pain. I tend to not push myself unless the snow is soft
Also there are just alot of instances where improving your skating is going to help your riding.
I'll be honest I gave it up almost 10 years ago cuz it just hurt too much - waaaaaaaaaaa. I was also roofing 60 hours a week and my body just did not enjoy the double time.
Now, I hike, its perfect for snowboarding, has no relevant skillset(for riding per se), but being able to grab your board and march to the top of the resort above the lifts on the first pow day without batting an eye is pretty badass not to mention useful. Also it keeps MOST of your muscles for riding in good shape (with the exception of all the little fuckers in your feet).
My core is fat and weak but I would add a core specific excercise or something to my regimen if I had all the time and gumption in the world, as it is not really built in any of these sports, but they all benefit greatly from a tight strong core.