Question: I know I could just carry a bottle, but scavenging is much more fun. What is a good source of vitamin C in the wild? Have spruce needles really got enough?

Answer: 
All types of berries are your answer here! Pretty much any (edible) variety contains a large amount of vitamin C - blueberries, strawberries, raspberries, blackberries for instance. (Blackberries and raspberries seem to be especially prevalent at the right time of the year here in the UK.) And they're tasty too.

Of course, it goes without saying if you're not 100% sure what a plant is then don't risk eating it.
[Scurvy Grass Sorrell](http://en.wikipedia.org/wiki/Oxalis_enneaphylla) has leaves rich in Vitamin C, and got its name from sailors travelling round Cape Horn who would eat the leaves to avoid scurvy.

It tastes pretty good, despite what the Wikipedia page says, but I'm not sure how widespread it is outside South America.