Don't buy ANYTHING yet!
You may hate flying, or as has been mentioned, not be able to pass a medical.
You won't need a chart before you do navigation, and it may have gone out of date by then. And people have personal preferences as to the type of pens they like, as you'll have gathered. though, personally, I'd buy Tesco nail varnish remover pads - you can put them in the basket without having to talk to anyone in the store, they only cost 99p, and they fit neatly in a pocket.
Some people like A4 kneeboards, others the smallest they can find, others none at all. Find out what you like...or you'll end up with three of them!
You will need the books for the exams and the confuser, but what's the rush? Unless you're planning to do the whole course in weeks rather than months. Air Law books get republished approximately annually, so will go out of date.
Unless you're the type to really worry about infection, don't get a headset yet - I've never caught anything in years of using communal ones.
You DO need a log book. Other than that, take along a clear head and lots of enthusiasm.
Have fun.