Very interesting to think about.

The book Artemis (andy weir, author of the martian) called digital currency "slugs" but didnt clarify the timing difference between Earth and the Moon.

My guess each planet/moon has its own currency. Transfer between planets takes 20 minutes, and thats just how it is. Cant really speed it up.

Taking hard currency (gold) would be too costly.

Possibly just taking some sort of hardware wallet with you on your journey.

Dunno man i wont be alive to see it 🤣