I posted this link on on the TCM Forum, but it is just too valuable to see it disappear after Xmas.
Lots of free (or cup of coffee priced) resources here and excellent advice on freehand sketching.
Just the ticket to form up your portable kit to create drawings to paint later back in the studio.http://www.peninkwatercolorsketching.com/
(Don't click here URL now dominated by commercial interests)
While you are in the mood download Russel Stutlers Sketchbook (Great Stuff).http://www.stutler.cc/other/sketchbook/sketchbook.html