Sketchbook - eg Seawhites (20cm x 20 cm perhaps?) ( bound or ringed) or Moleskin are another make you might like. If you already have a sketchbook or handmade one you like and you can devote it to this, fine!
Pen - permanent black
Watercolours (tho dilute acrylics could be used instead)
Blackwing palomino pencil (has eraser on the end)
Charcoal - willow sticks of varying size. Stick of compressed
Putty rubber. Rags.
Any inks, pencils, graphite, pencil crayons you have already.
Gesso or white acrylic. Range of acrylic colours tho you could choose to work in watercolours / oils ( oils aren't so good for sketchbook work but watercolours are ). Palette, palette knife.
Supports eg canvas boards/ paper/ canvas....suitable for working larger if you wish. Range of brushes.
2 canvas or canvas boards. (at least A3 size). One with acrylic burnt siena ground (reddy brown)
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 can have them or some equivalents it is helpful.
2 photo references or sketches of the sea (one with waves)
Brushes ( range of sizes but include a few 3/4 inch or so) Palette (as large as possible). Rags. Palette knife. Appropriate dilutant.
Pencil. A few bits of paper for sketching or notes.