You don't have to dress up for breakfast at the Marriott or anywhere else on St. Kitts - shorts and t-shirts will be just fine. I think there's a small convenience store just down the road from the Marriott where you can get coffee and muffins.

There's one beach bar (De Lime Beach Bar - not open every day) that's south of the Marriott (on the same stretch of beach) where you walk to for both lunch and dinner. You can find several other beach bars at Frugate Bay on the Caribbean side of the island (across the golf course) - they are about a 10 or 15 minute walk from the Marriott.

There's also a place right in the Marriott where you can get pastries/muffins and there is a convenience store as well.

We were at the Sunset Grill yesterday. Great but not fantastic. It is on the beach and the service is tops.
It is 1 mile away from the Marriottand the walk is all flat. A taxi would take you there for 5 bucks or less. The food is very American except the saltfish which I would stay away from. Very local and very salty.

Since we were at the Marriott recently, I was going to reply, but then noticed she said "early March". She is probably already there.