On Tuesday morning, I was at Barking station.
There was a notice on the closed, platform 5/6 WHSmith kiosk to say that
SSP - the company responsible for Millie's Cookies, Upper Crust,
Whistlestop and other food and drink brands at stations - has applied
for a license to sell alcohol from these premises.

I have enquired at <https://www.tfl.gov.uk/tfl/contact/tube/default.asp>
about the LU & TfL attitude to this.

Presumably, it is all right because Barking is a c2c station where LU
happens to run trains.

Has anyone got a list of stations where something similar applies?

From station addresses and service provision, I tentatively suggest the
following:
Amersham
Barking
Ealing Broadway
Heathrow Terminal 5 - unlikely given that photography is forbidden
Kensington Olympia
Richmond - SWT manages station
Stratford
Upminster
Walthamstow Central - bringing fond memories of Paul Corfield
Wimbledon - SWT manages station

If we have a summer in 2009, I can foresee some visits. ;)