Supermarkets were gridlocked with queues stretching back through the aisles at some locations as people tried to finish their grocery shopping.
One shopper said Tesco in Talbot Green was “manic”, with people waiting at the checkout for up to an hour.
In Carmarthen, queues of traffic were backing into the town centre.
Mike Wyn Davies said the Tesco Extra supermarket next to the Talbot Green Retail Park was busy on Monday morning.
He said there were such long queues at the checkouts that “the frozen produce started melting and had to be replaced”.
He added that staff were “amazing under difficult conditions”.
In Marks and Spencer in the Ty Glas retail park in Llanishen, Cardiff, checkout queues were taking about 15 minutes to clear.
In Sainsbury’s in Thornhill, Cardiff, shelves were almost empty, with pre-prepared vegetables and fruit in short supply.
Tesco in Bridgend was also very busy on Monday afternoon, with little room to manoeuvre in the shop or in the car park.
In Tesco Extra in Carmarthen, the car park was filled with shoppers fighting over spaces, with traffic backing onto main roads through the town, a BBC reporter said.
Meanwhile there were queues in the car park of Aldi in Plas Coch, Wrexham.
Several other shoppers took to social media to voice their opinions on the busy shops.