Funny how that is because on outbound Ryanair flights from the UK you tend to only see teas and coffee's being served on-board with some people brining their own food on-board. On flights back just about everyone orders food eg. sandwiches, snacks, hot food etc.
Why? Because the extortionate prices in airports in Spain and Portugal in particular make people buy on-board rather than in the airport, to the point where sometimes it feels like a big picnic event on the plane.
One must only assume that Ryanair passengers must be buying in UK airports. I certainly do! €2.70 for water on Ryanair? €4.50 for a premium sandwich? No Thanks! Just get a Meal Deal from Smith's in Stansted Departures.
€4 for water in Faro Airport? €6 for a bag of Malteasers? No Thanks, €2.70 and €3.50 respectively on Ryanair! See the trend?
I disagree with you JonEMA, Ryanair passengers seem to be very good at buying at UK airports because the prices are often lower than onboard. It's those who have inflight meals with Thomson, Thomas Cook, Jet2 or Monarch pre-booked that don't spend a penny.