A gîte week, the Loire by car or a month in the Alps
Paris for three or four days fits in the 3 GB pack, which runs for 15 days. Much of a French holiday, though, happens away from the capital, in a car and from one base: a rented gîte in Provence or the Dordogne, or a hotel in Tours for the Loire châteaux. A week like that, with the phone navigating country roads and pulling up château tickets at the gate, is a 5 GB trip, and that pack lasts 30 days.
When the rental has weak wifi or none, and the family's tablets hang off one phone, go up to 10 GB. The 20 GB pack covers a month: a ski stay in the Alps, a summer on the Atlantic coast or remote work moving from town to town.