This is what I always carry in my laptop case: a moleskine watercolour 13x20cm, a small watercolour case with 12 half pan colours, four different fountainpens with different inks (sometimes I add a Noodlers flex nib pen, but unfortunately it leaks lately), a pentel black paintbrush, some pencils and a water filled Koi waterbrush.
I also carry 2 red sable brushes; I had to cut the holder in half to make it fit in the pencilbag.
For neat works I have a decent Rembrandt watercolour set at home, and of course the other stuff like oil paint, acrylic and gouache, all types of inks, brushes, pastels and pencils.
Enough to keep me busy.
Only a month later, and this set was stolen from me, on our way back from a weekend in London.