The most obvious ones would be nuts! Hazel, beech (never found one worth eating though!), walnut if you're lucky, acorns after a bit of preparation. Berries such as blackberries are pretty much obvious to most, but there are others that you will need to look up on. Roots usually need some sort of prep in either cooking or pounding and drying or something complicated like that, so not really something you can just pull up and eat. I suppose carrots and the like you could, not sure how abundant wild carrots are though!
Beech leaves and hawthorn leaves can be eaten straight from the tree when they are young and fresh. Nettles too can be eaten without prep, although your tongue might sting a bit afterwards! Dandelion leaves can also be eaten when they are young and fresh, and ramsons can be eaten, in fact, the leaves, flowers and roots are all edible.
