Man of Honour
I was asked a few hours ago in a rather presuming manner if I will be taking my laptop on holiday "in case we have any problems we need you to fix while you're away" (I'm away in Europe for a week in May with friends - it'll be my first "real" holiday in two years).
"Sure. If you pay me an on-call rate every day I'm away or you pay me triple time on any day you do require me to work or you pay me commensurate to me effectively being available to you at all times...".
It's up to you how far you take this and what you do of course but I would not be keen to give up my holidays without a fair measure of recompense. I may not always have major plans for the time I'm away but I do know that I value the time away.