The Negombo coastal road is a trip in itself, running along the Hamilton Canal, it’s really beautiful and peaceful, as long as you avoid traffic time.
If you are taking the scenic cruise rather than hammering along the highway, the Club Restaurant is a nice place to stop. Basic beer and bite in semi-isolated huts, but the killer thing is the view.
You can wander out to the beach and see Colombo in the distance and waves crashing on the sand. Especially around sunset, it’s a beautiful view. And they have beer. Which is about all you could ask for.