Sheldon doesn't have a spot in the Cal Tech cafeteria?!
He's got his main spot at home, obviously. He claimed a 'spot' when he went to jail. He even said, "You're in my spot." when he corners President Sebert (sp?) in the bathroom.
However, I believe we see him sit in all four chairs at some point or another when they guys are eating in the cafeteria. And, to take it a step further.. they don't even sit at the exact same table every time.
Just a casual observation.