some kind of wire to make armatures - I'm using 1mm steel galvanized stuff that I got at the hardware store. Some people use paperclips, but I found they break very easily. The important thing is that you want your armature to be very stable. I was initially using 0.5mm wire and my models were flexing all over the place. The sculpting media is pretty thick, so you gotta use some serious force to get it on the model.
you will need at a minimum, green stuff - this is sold as Kneadatite. Do not buy it from "the army painter" or "greenstuff world", they repackage it in a hilariously small pack and raise the price on it a shit load. Apparently you can use "grey stuff" aka procreate as an alternative, but I haven't tried it so I can't vouch for it.
once you have the greenstuff, you've got options:
- mix the greenstuff with milliput - I use a 50:50 ratio and its really nice. Greenstuff on its own cures to a quite soft consistency, and you can't sand it. adding milliput makes it cure rock hard. you can