the other important thing to keep in mind is that in the EU in general, there's no added taxes on the bill, and tips are less of a thing here, so there's not a magical 20%+ hidden charge to factor in on everything you order.
We get signal wherever we can :) Boston Logan has about a 20-30% premium on normal groceries. SFO is probably closer to 5-10%. I assumed the premium could not be greater than 50% for Amsterdam airport.