2 canvas boards (at least A3 size) . Primed if using oil - just buy them ready primed.
Acrylic or oil paints. My palette for ref is titanium white, lemon yellow, cadmium yellow, yellow ochre, cadmium red deep, burnt siena, burnt umber, ultramarine, cerulean and viridian and alizarin so if you have them or some equivalents it is helpful - ie a red, blue, yellow, white and a dark or a brown to mix with dark blue to make a dark.
2 photo references or sketches of the sea or landscape that appeal to you and be prepared to play with it.
Brushes ( range of sizes but include a few 3/4 inch or so)
Rags. (t-shirt material is great).
Palette knife (with a 90% step is handy rather than totally flat and not too small).
Appropriate dilutant (no solvents please if using oils - I will provide sansodor or zest it if needed).
A silicon wedge Catalyst is a fun tool and a link is provided below if you wish to get one, though you could have a go with mine if you wish to try it first.
Palette (as large as possible).
Pencil. A few bits of paper for sketching or notes.
Silicon wedge link