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Audible is my main source for books - nothing beats audio books for all those hours when I just paint and paint and paint...
I own a Winsor and Newton metal watercolor case, a gift from my grandmother since she didn't use it anymore. (Thanks grandma! You enabled my young, optimistic self to take her hobby seriously!) Since this case is over twenty years old, I can't find the exact equivalent, but it's similar to this one: Winsor & Newton Water Color Half Pan 24 Metal Box Set * - but if you're someone who likes to carry their watercolors around (for travel sketches or just to stay flexible in general), if you're just getting started with watercolors or if you're looking for a less pricey option, their travel boxes are sturdy, too: Winsor & Newton Cotman Sketcher Pocket Box Watercolor Set *
MAKE YOUR OWN TRAVEL SET: I've been known to just stash my most-used colors in an empty match box (those large slide-out ones!)... with a bit of removable tape and careful arranging, this is the cheapest possible watercolor case you could wish for, and light as a feather, too. :)
Over the years, I've added to the colors that were in the set initially with a variety of new purchases, combining 'professional' and 'normal' watercolors (they all have their strengths and weaknesses - I'll do a color overview soon!) and different brands. My new favorites are actually by the Korean brand 'Shinhan' (available internationally) that offers really bright, vibrant and smooth colors in tubes: Shinhan Watercolors Artist Paint Tubes *. Mixing it up and finding colors that work uniquely for you is the fun part! You don't need to buy exclusively 'professional' or 'artist grade' colors.
Brushes I mostly get for cheap at local Korean art shops - I'll try to find out which of the best ones are available internationally!
My favorite paper for watercolors is hands-down the Fabriano Artistico Hot Press in Extra White *. Since the texture is so incredibly smooth and the white color pure, this paper is perfect for illustrations that need to be scanned and used digitally. There are barely any digital adjustments to be made if you want to get rid of paper texture, white-balancing is easy and the colors look vibrant and even, if that's what you're going for.
For small formats, I have this cute postcard format watercolor pad by Fabriano. *
For quicker pieces where visible paper texture doesn't matter (or actually adds to the watercolor aesthetic) I use Canson Montval Watercolor * paper.
Scanner: I use and love the Epson Perfection V330 Photo scanner. I've tried and owned a variety of scanners since before my art school days, and while this one doesn't allow for A3 scans (but has a large surface that goes beyond A4 for comfortable use) it is the most accurate when it comes to picking up colors, soft hues and transitions - perfect for anyone working in watercolor, colored pencils and generally light colors. It's also really affordable compared to some similar quality models I've tried.