Greeting shoppers in bright and colourful wellies and 'SOS' t-shirts, staff pulled out all the stops to raise as much as possible for the start of the campaign.
In Ballycastle, staff held a second-hand book sale and will be organising lots more activities over the 90 days.
Store manager Jane Steele said: "Our customers, members and staff have really got behind this campaign. The RNLI provides a vital lifesaving service for the area and we are very pleased to be able to support it. In just the first day we raised £220 which is a great start. All donations over the coming months are very much appreciated."
Over the past two years Co-operative staff and customers have raised over £54,000 through organising RNLI SOS day events making them one of the largest corporate supporters to respond to the charity's SOS.
John McNeill, The Co-operative's Regional Operations Director for Northern Ireland, Scotland and the Isle of Man, says: "The RNLI provides an invaluable service and is a charity close to the heart of many of the communities The Co-operative serves. Our big-hearted staff, supported by our ever generous customers, will go all out to raise as much money as they can for such a deserving charity."
Caroline Mason, Corporate Fundraising Manager for the RNLI in Ireland, says: "We are delighted to be working with The Co-operative, who like the RNLI, are a large organisation with a community focus.
"Their staff have an infectious enthusiasm, and like our volunteers are community focused and extremely charitable. As a charity we rely on donations, and the £90,000 The Co-operative aims to raise will help pay for a years training for 59 of our volunteer lifeboat crew in Northern Ireland, Scotland and the Isle of Man. "