The head of Retail Excellence says shops won't get 'a second bite of the cherry' for supplies this Christmas.
Duncan Graham was speaking as experts warn global supply chain issues - around the pandemic and Brexit - will impact Ireland.
He says latest figures indicate some 80% of products were moving smoothly from Britain into Ireland, and that some members have moved supply bases away from the UK.
But he told The Pat Kenny Show people will need to shop early.
"This year feels as though it's different, this year feels as though certainly there are some added problems.
"If you look at the actual supply chain, it's a finely tuned machine - and when you lock in a pandemic, and the fact that people and countries have been locked down for significant periods of time - really what's happened is we've had a massive plummet in terms of demand for products.
"And then of course we've opened up and there's a huge surge of demand for things as people have gone out and spent".
He says there are also issues around reduced capacity at key ports, such as Rotterdam, and even COVID-19 cases on ships in ports delaying their unloading.
"It's certainly impacting across the board at the moment".
He says a lot of products we rely on have to travel a long way to get here.
"If you think about what's under the tree on Christmas morning, a lot of those products are coming from the far east, they're coming from a long way away.
"And those are the types of things that we're going to have some difficulties with.
"Things like toys, electrical items, Christmas decorations even and clothing items - all of those things could be impacted.
"I'll caveat that by saying I still think there's going to be plenty of products out there, it may just not be the stuff that you really want.
"The real message has got to be if you want something, you see it in the shops now, buy it now - don't wait until that final week before Christmas".
And he says people should have a back-up plan as they shop.
"It becomes fairly evident early on which products are going to sell out and which products are going to be fast.
"And retailers quite often have a second bite of the cherry to be able to go back and re-order stock that's manufactured quickly and get that in pre-Christmas.
"This time around, because of the delays, that isn't going to be happening.
"I think the message to consumers will be 'have a plan B' - if you can't get that plan A, have a plan B and be prepared to shop around".