You can prepare as much as you want for disruption, but not everything is within your gift to control. Particularly with supply chains. What might the increased cost be? Can you afford it? Can the alternative arrangements meet the requirements of your business?
There are so many spinning plates in the event of Brexit, that it's hard to properly prepare for them all. Especially if, as is the current case, much of the preparatory work is being done through central government - who are largely directing local systems to 'prepare' for every eventuality, while simultaneously asking them not to take any action aside from having faith that work is being done.
The NHS medicines management being an example: local request is to source alternative medicines and rely on continued supply, which will continue as normal, as a result of government arrangements.
Those arrangements have so far been Seabourne Freight and now DHL.