I use organic topsoil for practically any tropical/subtropical setup, typically Scotts from Home Depot (the red, slightly pricier bags) due to its "fluffier" consistency and ingredients, but most organic topsoils seem to be alright.
Also a good couple handfuls of moss; used to be able to find sphagnum moss in bags at Lowes every now and then, but all the stores near me stopped carrying it a good number of years back; they sold it in large blocks as "orchid moss" or something of that sort (stuff would have a ton of pine needles or something mixed in, though). I now just use shredded dried sheet moss (NOT preserved; I don't trust whatever happened to it to make it permanently green), which works alright, but still doesn't beat sphagnum IMO.
Possibly a handful of sand or two; typically Quikrete Play Sand (same stuff I use for my tanks; easily washable, good grain size IMO).
And a bunch of random botanicals- typically whatever random stuff I think is safe and suitable that I find in places relatively untouched by human influence, such as leaves, alder cones, pieces of oak bark, maybe some small twigs (from deciduous trees, and safe ones at that); I usually use a small hand rake to gather it up. Sanitisation usually involves stewing the lot in a big pot.
Oh, and dead leaves (or sometimes the whole plant, broken up or intact) from safe houseplants that I always manage to kill.
I sometimes toss in a few P. pruinosis as well; if I do, I add some ground cuttlebone and bits of snake shed.