CNN posted a lovely infographic of something the British government barely mentioned thus far.
UK relied on EU for external trade and cooperation treaties for decades. Once out of EU the treaties will no longer apply. UK needs to figure out which ones it needs and which ones it can do away with and renegotiate them. There are over 600 treaties with 150 states in total, I guesstimate UK needs about 100-150 of them.
Given that the country was forced to import negotiators from New Zealand for Brexit, I foresee a series of miserable failures on this front.
http://money.cnn.com/interactive/news/economy/brexit-treaties/
McHrozni