To sum up, here is what I personaly use as a basic equipment:

1. a 300g/m² (140lb) watercolor paper ARCHES, 56 × 76 cm, 22" × 30" to be cut
2. three ROWNEY Artists' Water Colour tubes:
   
   • aureolin yellow n°601
   • cobalt blue n°109
   • Rose doré alizarin n°560
     
3. three brushes of any matter (synthetic or natural)
   
   • diameter 4-5 mm
   • diameter 6-8 mm
   • flat brush 10 mm or more to wet the paper

Regarding the material, I think that's enough (in fact you need also a pencil H or HB, a kneaded eraser and a water pot - a seat for outside work may be convenient).