I use various good quality watercolour papers, usually 300 gsm (grams per square meter) so that they do not distort when wet. I prefer working on watercolour blocks with gummed edges such as those produced by Winsor and Newton, Saunders Waterford, Fluid and Arches.
I use sketchbooks published by Moleskine, Strathmore, Seawhite and others, again only using those with good-quality watercolour paper.
I use a mixture of Winsor and Newton (W&N) and Daniel Smith (DS) watercolours and my current palette is as follows
Buff Titanium (DS)
Light Red (W&N)
Raw Sienna (W&N)
Raw Umber (DS)
Lunar Black (DS)
The Winsor and Newton Light Red and Raw Sienna are irreplaceable colours to me. I've tried other Raw Siennas but the W&N has a particular quality of light and luminance which think is unique.
Light Red is a basic colour for all brickwork and for mixing with French Ultramarine to make a vast range of greys.
Butt Titanium is so useful for buildings - particular the many buildings in the Loire Valley made of Loire Stone and also London buildings made of Portland stone.
Lunar Black is a really useful colour - so heavily granulating which I love, and also great for things like car tyres or other patches of deep, matt black.
Sap Green is very useful as a starting point for a whole range of greens. I know I could mix greens from blues and yellows but I like to start with Sap Green. Perylene Green also is so useful for those patches of dark green shadows in summer trees, particularly when mixed with French Ultramarine for the very darks.
I find that sable brushes hold a little too much water for my small paintings and so prefer either nylon brushes or a sable/synthetic mix. At the moment I have a set from Rosemary and Co of sable/synthetics which are just fine but to be honest anything with a good point and fine watercolour hair is fine.