I can highly recommend that you go into a co-operative store and do your shopping there for most of your essentials. They have a great selection, good daily specials and you can buy the vegetables loose. There are Marks & Spencers in some places which are of course the high quality you expect.
For meat try a local butcher – they might be a bit pricier, but the quality is worth it!
If you are in Portree on the Isle of Skye, pop into Relish and Cathryn will be more than willing to assist you. Call the shop on +44 (0) 1478 613787.
We love Thorntons for their toffees and sugar free chocolates.