Well,it's really important topic!
After driving 8 months semi truck every year I need really good conditioning for few winter months. I start preparing myself from first day of august with running 2,3 times week for few miles. I got few things in my truck(exercise mat,ball ,resist.bend and jumping rope) and doing push ups,different exercise with things above and legs(squats,lungs,jumps,squats on one leg),abs...
When I get back to Europe around Christmas I start with gym and some weights and getting ready for season. Let's say that I can ride 200-300 hundred km of slopes in day or two on my free ride in fast tempo.
I start riding hard boots last year and can do all day without issues,I feel more safe and strong with good pre season.