if no deal on 29.3.19, my predictions for 30.3 to 7 April (and beyond):
Lorries... this whole lack of ECMT permits, whatever they are called. UK may choose not to check lorries entering from EU, but EU will check lorries entering from outside EU. So OpStack on our side of channel. Ferry services running late, goods being transferred at EU ports onto other lorries authorised to operate in EU, all sorts of schedule delivery disruptions.
Starting after about 10 working days: Factory assembly lines in EU just stopping due to lack of parts (made in UK); followed swiftly (within 2 months) by cancelling those orders from UK suppliers & (within 4 months) massive job losses in the UK manuf. sector.
(if Uk does let EU goods without checks or tariffs etc, but still checks r-world goods). if sustained more than 2-3 months, Several cases being launched with WtO by non-European countries about UK violating WTO rules & giving EU preferential treatment outside a trade agreement.
Fisheries: suddenly couldn't land most their catch in EU or get it shifted in time; literally tonnes of rotting fish, or fish that would have been very high grade going into other products instead, being dumped in UK for peanuts prices, or degraded value in EU. Would lead to mass redundancy & sector downsizing within 5months if not resolved.
Within a month, Lots of news stories about UK tourists & some UK nationals resident in EU being caught out by roaming charges, wrong driving license, lack of medical insurance.
Lots of extra activity at ports as emergency stock ferries arrive and there is oversupply in some types of goods. Warehouse storage in Uk will continue at or over official capacity.
After about a week, News stories about panic buying.
Plus I think a lot of legal fudges that allow planes to fly etc. without meeting the actual legal rules that should enable those things to happen.
Sustained: Constant constant constant news about the chaos & disruption in these & other sectors. Lots of news stories about organisations breaking what few rules may or may not apply (employment, trade, etc.) Huge numbers of small UK businesses caught up in the mess who had no idea they would be affected.