All they have to do is hold things up for an extra 24 to 48 hours to raise hell with today’s logistical system. You have to stop thinking Zombie Apoc and realize you won’t be going full Mad Max. But delays cost money, and shrinking profit margins cost jobs.
There's been no mention of export controls at the continental channel ports.
The only reason for any delay would be due to checks in the UK & I cannot see them being imposed in the immediate aftermath of a hard exit.