Apart from the real essentials like changes of clothes, appropriate clothing for the weather, toiletries and medication, what would you take on holidays that others might not?
I always take a wash cloth – because you never know where and when you might need to freshen up, and a one-size-fits-all sink plug. I also carry a couple of small containers of good instant coffee – real and decaf – because the stuff in budget hotels is usually undrinkable.