When I was working, holidays and other things were agreed at department level. Mrs. L worked in school admin and her holidays were fixed, so as long as I could get time off during the school holiday period, that was fine. Generally, priority was given to staff with young families and this also suited the older / younger staff who wanted off peak holidays.
Holidays usually consisted of taking the motorhome to Europe - a lot easier and cheaper when we lived in Hampshire. I never booked the ferry more than a few weeks in advance, and never booked camp sites in Europe.
The only time I booked well in advance, was when we had our road trip across the USA. Even then, we only booked the flights and the ferry crossing across lake Michigan. Everything else, we just planned day at a time.