I have two....
Like someone else said, the bench of the equipment I'm using has to be lined up perfectly so it's parallel with the walls, or the lines on the ceiling/floor. If I'm doing bench press and the bar isn't parallel with the lines on the ceiling, I feel like I'm using one arm more than the other....
Also, I have to get up and have a drink from the fountain after every set.... if I don't, I feel.... well, I guess it's more of a habit than a superstition. Probably nothing wrong with it, except sometimes I lose my place on the equipment.