@MissionItsPossible
Will there be sufficient food and medicine?
The government's own assessments suggest not. The NHS is already spending millions of pounds and hours of valuable manpower preparing for such an event. Food is predicted to run out within a fortnight (the UK only carries a buffer stock of one-weeks worth of food, which will disappear as soon as The Sun or Mail reports panic buying in the supermarkets).
Will all imports and exports stop if the ports clog up?
The head of the Port of Dover thinks so. The logistics companies think so. If there is a Hard Brexit, all 750 agreements that the UK has become null and void, so there is no legal basis under which goods can dross into or out of the UK. WTO rules only kick in after the UK has reached an agreement with the WTO members. UK hauliers lose the right to carry goods into Europe. There are just over 100 licenses available to non-EU carriers, but 10,000 lorries leave the UK every day.
Even if an interim agreement can be reached, a delay of just 2 minutes per lorry (compared with the current 'arrive and drive' arrangement) will result in 17-mile queues on either side of the Channel.
Will Nissan, BMW, Airbus etc begin moving out of the UK?
Who knows? BMW have said that production in the UK will end on the day that free and frictionless borders end. Airbus have said something similar. The Japanese Ambassador (on behalf of Nissan, Toyota etc) has stated the obvious fact that no business can operate in a country if it cannot make a profit. A million workers in the UK are hoping that these and other companies don't close their UK factories.
Will investment pick up again?
With no export markets to serve and domestic consumption collapsing, I see no reason why it would.
Who will benefit if the pound falls?
Not the general public, as prices would rise by 20-30%. Maybe the fund managers and gamblers who are shorting the pound. Somebody must be due a windfall - perhaps we should look at who the loudest Brexit cheerleaders are.