Milk, Eggs, Butter, Fruit, Veg, Flour, Cereals where possible (certainly Porridge oats and weetabix (well Sainsbury's own) and cornflakes), Meat, Christmas pudding , tinned pulses and tomatos, pasta, rice, I think that covers most of what we buy tbh.
I think as belts tighten, we will have to switch back to non-organic varieties (I go on maternity leave for a year in Jan for a start!), but there are some things that experts say you should always aim for organic varieties-
Milk
Meat
root veg
Berries
I think were the most important. I would rather eat smaller quantities of meat than have to eat factory farmed chicken for example- and we're happy to have a few veggie meals per week if thats what it takes to economise- though to be fair organic fruit and veg are usually pretty expensive, especially if you don't have access to local farm shops etc.
The 'farmers' markets' where we live are in reality small producers markets- so honey, jams, cheese, sometimes meat...but rarely a wide variety of veg or fruit- perhaps peas when in season or rhubarb, but thats about it.