If in Europe, if you don't have included roaming, most MNOs offer roaming add-ons.
Outside of Europe, better value is to pick up a local SIM on arrival, and buy a bunch of data.
What I do when travelling outside of Europe with family, is that I take a mobile hotspot and put a local SIM into that, and then allow the rest of the family to connect to that. The advantage of this is that you control the connection - everybody else has their phones set to no roaming (and therefore no risk of uncontrolled cost), and you can topup as required. I have a NetGear AirCard - has a swappable battery so you can keep one spare fully charged.
If in Europe, if you don't have included roaming, most MNOs offer roaming add-ons. Outside of Europe, better value is to pick up a local SIM on arrival, and buy a bunch of data. What I do when travelling outside of Europe with family, is that I take a mobile hotspot and put a local SIM into that, and then allow the rest of the family to connect to that. The advantage of this is that you control the connection - everybody else has their phones set to no roaming (and therefore no risk of uncontrolled cost), and you can topup as required. I have a NetGear AirCard - has a swappable battery so you can keep one spare fully charged.