It likely contains white pads on top (toss these) and then some rigid media, ehfisubstrat or noodles or something like that, then some coarse pads. The pads and the rigid media can be used over and over again, for many years. I would consider using boiling water on the rigid media and nuking the pads for maybe 10 seconds to be sure there is nothing iffy carrying over. Chances are there is nothing scary residing in there but you never know.
I do not buy the expensive white disposable floss pads, but I use regular poly filter floss in the bag, and just stuff a wad of it in the top. I've been doing that for years without any difficulty.
Edit: There may be a carbon pad in there and I'd toss that, as well, as it is no longer functional, other than being a place for biobugs to reside.