A stop at Bluefields Bay Park would be perfect for all your needs. There are a couple of restaurants there and it's a good place to chill. Fresh fish was on the menu the last time we were there and the lobster was really good. We stayed and had a few beers with the restaurant owner. I can't remember the name but it has concrete table and chairs. That stop would be about half way between Black River and Negril, maybe a little further towards Black River.
You could also try Cloggy's in Black River for a stop. Nice restaurant right on the ocean. You can see the odd croc swimming not to far from shore. For lunch you pick a freshly caught fish out of a cooler. Lobster there was really good as well, but don't be in a hurry.