Last exam I took:
1 x calculator (even on an essay exam - my calc ability turns to rat sh*t when I'm stressed)
Pencil case full of pens/pencils (knowing me, if I took just 3 pens, they'd all stop working)
A mini clock (to make sure I can see the time I have left, even if they stick me so far down the back I can't see the exam clock)
A mega cup of Starbucks coffee (in case of coffee withdrawal in the middle of exam)