I would be very surprised if businesses were not looking at how they could mitigate any disruption - resourcing their ingredients within the UK where possible, changing their menus to using more seasonal products etc
Of course businesses are looking at how to mitigate disruption, but in respect of food, the UK has not been able to feed itself for around 200 years (which is why around half of the food eaten in the UK is imported) so sourcing ingredients from the UK and changing menus to seasonal products will have very limited success.
I personally don't think it would be a bad thing if we really had to rethink about what we eat and when. The carbon foot print of so many of our food stuffs is astronomical.
I don't think anyone will disagree with you on this point, but the fact remains that food has to be imported as the UK has relied on food from abroad for centuries. The last time that this supply was disrupted was during WW2, when every square inch of available land was used for growing food, and there was still nowhere near enough to feed the population without introducing severe rationing.
If there is a no Brexit then we will know about it in advance, unlike sudden changes in the weather or unknown shortages which are exacerbated by everyone running off to buy the last loaf.
I assume you mean a No Deal Brexit. The UK is now just over 3 months from Brexit-day on 29th March but still nobody knows what the plans are for leaving the EU. Hard Brexit? Transition period? Who knows.
One of my largest clients is a haulage company that brings in fresh food from the EU for a UK supermarket chain. They don't know what is happening after 29/3. In the event of a Hard Brexit, i.e. No Deal, then the business will require a permit, the drivers will require new commercial licenses and the vehicles will require new certifications. They will also require access to the HMRC system that is still being developed, and staff will need to be trained in the new customs clearance procedures.
There is no clarity around any of these issues, making it impossible for him to plan with any certainty. If permits are required, they will be competing with 10,000 other hauliers for just over 900 EU permits. They have no idea how they will get the drivers and vehicles compliant by 29th March - even if they get the definitive information tomorrow, there is too little time to achieve this by 29th March. They have had no sight of the any new customs IT or procedures, so cannot recruit or train the required staff. Finally, if the RHA estimates are correct, and it takes hours to clear each truck through customs in Calais and again through Dover, his vehicles and drivers will be facing queues measured in days. The business only makes money when the wheels are turning - having trucks costing £200k each sat idle for days will put them out of business in a matter of months.