physically 
I keep binders for each of my characters, with character sheets, notes, and print-outs of any relevant sections of books (class description, abilities, spells, etc). it saves my back from having to lug around a bunch of books when I can just slip a binder into my backpack instead along with my dice bag, pencil sharpener, and a couple pencils.
less directly game related, I also bring drinks for myself and snacks for the group/host.

I keep binders for each of my characters, with character sheets, notes, and print-outs of any relevant sections of books (class description, abilities, spells, etc). it saves my back from having to lug around a bunch of books when I can just slip a binder into my backpack instead along with my dice bag, pencil sharpener, and a couple pencils.
less directly game related, I also bring drinks for myself and snacks for the group/host.