What about vacation days on retirement?

You can either agree with your employer that you will take your vacation and comp days in the form of time off before you leave, or that you will receive them in cash. Usually you'll get the money in a lump sum, but I'd advise you to discuss with your employer whether they can split it up in some way, if that's what you want. However, they are not obliged to do so, but they have the right to pay everything in one lump sum.