As already mentioned in Welsh words for fruit, a supermarket initially appears an unlikely environment for language learning. But first appearances are deceptive, and you have plenty of opportunity to practice your Welsh (silently perhaps) as you carry out your weekly shop.
How about using Dw'in lico ... 'I like ...' and adding the appropriate food word (in Welsh) as you roam the aisles looking for bargains?
Dw'in lico coffi or Dw'in lico hufen iâ
An on a food theme, have a gander at the names for the Welsh Vegetables, Meat and Holiday Phrases.