I think you’re thinking too much. More than likely they’re not thinking about you, and if they are then screw them. Same thing as when feeling self-conscious at the gym.

Besides, for all they know you’re a graduate student. Perfectly normal to be your age with a backpack. I’ve been out of school for four years now but still prefer to pack my stuff in a backpack when working from cafes and the like.

I like working at Koffee? and The Coffee Pedaler when I need a change of scenery. The public library is good too.