1. Flesh 5 A-C: Unless I'm painting orcs, this triad is always in my kit. Sometimes I use Terracotta 37A as a base to create extra shading before Flesh A.
2. Boneyard 9 A-C: This is a favorite alternative to white for tunics and breeches. I use this for lots of different leather items, drum heads, blond hair, etc. It's also great for bones, fangs, and claws on fantasy models!
3. Rawhide 11 A-C: I use this triad for boots, belts, hats, etc. There are lots of good earth tones in the Foundry line, but this seems to always be in my kit.
4. Spearshaft 13 A-C: I use this for boots and other leather, hats, hair, muskets, and, yes, spearshafts. I also frequently use it for horses.
5. Winestain 15 C: This jar of paint will last me forever - I use it to paint the bottom lip of all of models. This little touch of color adds a lot of life to the face.
6. Slate Grey 32 A-C: This one of my staple colors for neutrals, used for trousers, hats, pouches, etc. If I want a rough and tumble look for a model on campaign, I use A and B to add a five o'clock shadow to the jaw. I also use Slate Grey C as a base for white...
7. Arctic Grey 33 B: Like black, I rarely use more than one highlight for white areas. Maybe if I were painting a unit in parade dress or Imperial Storm Troopers I'd add a layer of pure white, but I don't normally carry it.
8. Charcoal Black 34 A and B: Unless a model is predominately black, I only use one highlight layer when I paint black.
9. Terracotta 37 A-C: Seems like I use a little bit of red on everything I paint! I tend to use muted tones in general... terracotta rather than red, ochre rather than yellow, etc.
10. Boltgun Metal: I have a full set of Games Workshop paints on hand, but this one is the only one that is a permanent part of my kit.
These are the foundation of everything I paint. Other colors may be dictated by a specific uniform or simply a whim, but I try to maintain a limited palette so I keep this to two or three extra colors when possible.