It's about finding a middle ground between not taking everything and not taking enough/wishing you had something. For me, I sit down and think about our current day or how we behave in a current space (we don't live near a beach so I have to think about what we look like there). I walk through our day. What we use at home is what we will on vacation. If we don't use it at home, I don't waste my time bringing it on vacation.