without wishing to deviate OT. Easyjet carrier regulations do state in section 10:
Carrier's Regulations | easyJet.com
In addition to the “Standard Hand Baggage” you may also carry:
(a) one of the following: An overcoat; an umbrella, or a shawl; and
(b) one standard size carrier bag of goods purchased from the departure airport.
whereas Ryanair:
General Conditions
Strictly one item of cabin baggage per passenger (excluding infants) weighing up to 10kg with maximum dimensions of 55cm x 40cm x 20cm is permitted. (handbag, briefcase, laptop, shop purchases, camera etc.) must be carried in your 1 permitted piece of cabin baggage.
So any notice in the airport about duty free carrier bags being allowed would appear to be in contravention of the ryanair terms and conditions