The following are suggestions - my favorite or most used supplies.
Feel free to bring what you have, or your favorites though.
Choose a journal that you'd like to work with. This could be anything from a bound sketchbook to a 3-ringed binder. I've used:
Hardbound Canson sketchbooks
Moleskines (with either drawing paper or watercolor paper)
Stillman & Birn sketchbooks (current favorite: Delta series - has cream colored watercolor paper).
Pencils - I use a combination of mechanical pencils or Tombow Mono pencils. Bring whatever you like using though.
Pencil sharpener - handheld or electric
Erasers - I use both kneaded erasers and white erasers
Pens - my favorites are Microns or Copic (various sizes).
For color -
I use a travel watercolor set from Windsor Newton
Favorite brushes: Black Velvet #6 round, American Painter #1 bright
Prismacolor - colored pencils
Primacolor Verithin pencils (black and brown)
Double sided tape
Small plastic triangle
Anything else you'd like to work with!