I was in Boots on Princes Street the other day and there were leaflets saying that from 1st August to 31st October, it you buy 5 meal deals for £2.99 during a calendar month then your 6th meal deal will be free.
All you need to do is make sure you use your advantage card with each purchase and your till receipt should detail how many you've bought that month.
The leaflet said the offer was only available in selected stores and all the stores listed were in Central Scotland (Edinburgh, Glasgow, Fife etc), but this might be available elsewhere in the UK with only local leaflets being printed??
It's not a huge saving but not bad if you already buy your lunch there most days.