[msc]

Just got myself a used XP1 filter. No media came with it. So the question is what to stuff the basket with?

 

[Aubzilla]

Anything you want.
That's the beauty of canister filters.

 

[Darkblade48]

Buy some coarse mechanical filtration media (i.e a coarse filter pad), then some biomedia and finally finish off with some fine filter floss.