Surface: I recommend a 9”X 12” or any size watercolor paper. Watercolor Paints: Pan watercolor sets  (a basic beginner set is fine)   Do not buy sets at the dollar store- they can be low quality.  
Paint Brushes:  A larger flat  brush 3/4″ to 1″ wide, a narrow round brush to paint details and thin lines.
Palette: Paper plates or scrap paper work just fine.
Water Cup: Plastic cup or one that you don’t mind getting covered in paint.
Paper Towels: or an old rag for cleaning the brushes