Even when I'm on a personal overseas holiday, our agreement is that they can certainly ask me to do things on laptop (always goes with me) and once I even got diverted in Sth America to go to Canada, forgoing a wine tasting in western Argentina for a very urgent task. Another time I flew myself to San Diego for a big conference and spent the entire 4 days in the hotel room working on another urgent job. Got to give my talk and also go to the conference dinner, though.
Mind you, this type of service does come at a cost to said client

. Not complaining, just observing.