Being a GM and a player, I do take very different things to my gaming sessions. As a GM, I run , so I need a fair number of supporting documents - new rules to playtest and the usual kit: dice, paper (squared), pens and a hard back book I record the campaign goings on in. We don't use minis. I tried to use minis for Icar but that turned into a farce - the game is far too dynamic for that. I don't use a GM screen, there is no need for it and the players don't need the rules except when choosing new skills.
Oh, and I take food and drink. The host provides cups and glasses but we don't call upon him for anything else.
As a player, I just bring my dice/pencil case and if we're playing a game for which I own a rulebook, I'll bring that.
So, what about you? What do you take.