Travel brushes make taking your brushes anywhere much easier as they don't take up so much space! The 'handle' comes apart and slips over the brush bristles to protect then while in transit (or even in your pocket). They're ideal for taking to workshops, on holidays, and for painting on location.
Painting with a knife is quite a different experience to painting with a brush. Not only can you produce a range of different marks, but it feels distinctly different in your hand too, a bit like spreading jam with a really springy knife. If you've never tried one, I'd go for a mid-size painting knife with a flat top and a sharp point on a corner because this enables you to create large areas of color and small details. See Also: How to Use a Painting Knife
A Colour Shaper looks like a brush with a flexible tip instead of bristles, but you use it more like you would a painting knife, for pushing and smearing paint around. They're great for texture effects, and for sgraffito. Color Shapes come in a variety of shapes, sizes, and degrees of flexibility.
See also: Intro to Art Brushes: Colour Shapers
I believe that even before you've put an image or word into it, an art journal needs to be a thing of beauty. Something you want to hold, that makes your fingers itch to fill the pages. Fabriano's artist's journals come with either cream and white pages, or in a selection of colors. They've also got a ribbon so it's easy to find the page you last worked on.
See also: Art Journaling
I invariably have a pocket-sized Moleskine with me; which one depends on where I'm going. It could be the blank sketchbook (which doesn't really like watercolor paint), the storyboard one (perfect for thumbnail sketches), or the one with watercolor paper in it (the individual sheets are perforated so you can tear them out easily).
The rounded corners mean that if you shove one in a trouser pocket, you don't get sharp corners digging into you. With a Moleskine and a pen (or even better a brush pen (buy direct), art can be made anywhere. (Be warned though, while Moleskines don't have covers made from mole leather, they do have leather covers so may not be appreciated by a strict vegetarian.)
A small book light is perfect for working in your art journal or sketchbook at night when you don't want the light to disturb someone else, or if you want focused illumination on the page only. Depending on the model, a book light either clips or slides into the pages. Most run on penlight batteries, some are rechargeable.
I find few things handier than a "holds almost everything" container for keeping all my art materials together for workshops or when I take some paint supplies on holiday. One that will take my paints, brushes, a small paper palette, sketchbook, cloth, water bottle... though not quite the kitchen sink.
If you prefer a storage container that allows you to organize and sort your paints / art materials, go for one that folds out with multiple trays. Just remember that when it's full, you'll need to be able to pick it up!
Say goodbye to worries about getting paint on your clothes with a lab coat. In fact, in its pristine state a lab coat is rather ugly, so getting some paint on it can only make it look better.
Art and Fear: Observations on the Perils (and Rewards) is a small book (only 134 pages) without any photos or artwork in it, just words. But what powerful words. I think it's something every artist ought to read, not just for those days when you doubt what you're doing is worthwhile, but as a regular boost of motivation and confidence.