Sometimes you need just a little extra space to make precisely the shade you need. I carry a Mixing Palette to take my colors a little further, keeping the pans free from paint with the exception of adding a fun color or two in the smaller standard pans, like white gouache, and a black or neutral tint.
My palettes usually look this messy! Mixing colors is just so fun, putting together a little of this and a little of that. When it's time to go, I usually just close the lid and move on.
Coming back, the colors on my palette can be a starting point, often "palette grey." If I need some fresh space, I'll wipe them with a wet brush and towel.