I may be wrong but I don't ever recall being asked, even once, to show my boarding card in airport shops like WH Smith or Boots? In the Duty Free every time but not elsewhere airside.
WH Smith are bandits of the highest order - same on motorway service stations - absolute ripoff prices for sandwiches, soft drinks etc. The one I use most is halfway ish between Harrogate and home. WH Smith Northbound or M&S Southbound. So when travelling home northbound I walk across the bridge.