Nothing in particular to get started on the drifting (you'll want LSD or a welded diff though). All you do is book (£70 for santa pod day) and turn up! Ideally take lots of tyres with you but they usually sell part worns there.
It's a fantastic day IMO, I'm going up on 5th Feb in my e36 (assuming I manage to replace the drive shaft, it snapped and is pretty much welded into the hub).
There's loads of info on driftworks or the santa pod website itself for DWYB (Drift What Ya Brung).
Bucket seats/harnesses/stiffer suspension/hydraulic handbrake all help but none are vital. They're probably more important in that order but it's all personal preference, and not needed to have fun at beginner level