Men's shirt collars can have a mind of their own. If left to their own devices, they may curl instead of looking starchly in place. If one is wearing a tie, then one has to make sure the collar stays where it's supposed to.
For that, there are bones (as they are called in my house), also known as collar stays. These little doohickeys can work wonders just by being slipped into the shirt collar.
They are available in both plastic and metal. If getting plastic, make sure they are solid and firm; they shouldn't bend or fold while being slipped into the collar.