I've got a couple of days off, 2 kg of sculpting clay, and zero previous experience of sculpting. What should I make?

Mushrooms. The first few will probably be pretty rough, but you'll quickly start to see the possibilities with different textures, shapes, adding gills underneath, etc. If the clay is different colors you can get buck wild. After fewer than you think you'll probably be pretty good at them. You can even screw in a hook at the top and turn them into ornaments for friends and family if that's your thing.