I understand what you are saying, but rollerblading not required.
Things I think are effective for cross training (effective for me means using it to help with trying to have somewhat balanced muscles even though I rarely skate switch, increasing jumping ability, increasing stamina):
- Hiking/rockclimbing-- helps balance, strength, conditioning. Healthy to be outside.
- "skater yoga"/wheel and foam roller and Matt stuff- helps with strength and flexibility + recovery
- Pull-ups and burpees-- helps with strength--bert slides and falling are key.
- Push ups including on fingers, sides of hands, etc.-- increases strength and bone toughness for falls (maybe)- helpful for Bert slides.
- Biking (for me, this means a 26 inch bmx bike-- others prefer road bikes, fixed gear or mountain bike-- I shouldn't have to explain bikes to anyone. I like doing dirt trails, mild downhill. I find after I bike a fair amount I both shed a bit of fat which helps for skating and get my jumping strength up as jumping with the bike is both easier than on a board of course (just chucking off dirt jumps) but also works the muscles-- both legs and pulling the heavy bike up
-Snowboarding
- Sports wise- As a kid I was keen on basketball as most applicable to skating cross training-- now I stay away as tend to get similar ankle injuries in basketball as skating. Floor hockey has similar explosive nature for training purposes (or if you want to keep blading, some roller hockey)
- For those that can-- skim boarding, surfing, swimming, body boarding - shouldn't have to explain why these are good for strength, balance, stamina.
As others noted, this is a well known thing, and of course just walking, lifting, whatever would help, but this is what I think as an older guy helps me get into skate shape. I should probably add some jump rope and more cardio/stretching, but oh well.