British businesses probably didn't expect to start 2021 worrying about wooden pallets after a year of grappling with the coronavirus and a meltdown in the economy. Yet as they start a new relationship with the European Union (EU), securing a supply of heat-treated platforms—baked to 56 degrees Celsius (133 degrees Fahrenheit) for at least 30 minutes—is now one of the myriad issues they face.

The 1,200-page trade deal struck by Prime Minister Boris Johnson on Christmas Eve after a little over nine months of negotiations ended the uncertainty that the U.K. would crash out of the bloc in chaos. While the zero-tariff, zero-quota accord is a relief for British companies, it only marks the next stage in the evolution of the Brexit process—and potentially the most difficult one.

Be it wooden pallets for shipping goods, customs paperwork, new fish quotas, or the recognition of professional qualifications, the next few months will be a case of figuring out the consequences of not just what's in the historical agreement, but also what's not.