I keep my palette moist by spraying a fine mist
of water on it about every 10 minutes or so.
It’s a used lens cleaner spray bottle.
Hope it helps you.

I notice that Gurney sometimes put his gouache on a slightly damp paper towel segment. I only use white gouache with watercolors but keep my white on a damp towel on using a mister occasionally. The downside is that it can get too damp. It is dry (not humid) here and that seldom happens. Gary

Pretty much what everyone has suggested. I have the stay wet palette, and didn’t like the absorbant paper at first but am use to it now and it doesn’t bother me, I can blend just as good as a porcelain palette, once I started using gouache thicker, I realized I don’t need the smooth mixing surface of a porcelain palette, and I just use a water mister and spritz away. Another thing that helped was when I add the paint from the tube onto my mixing surface I try to make sure I have little lumps, instead of short little smears, which tend to dry out more, but I really don’t mind the consistency of reconstituted gouache, so it’s not a huge deal for me unless I need a thicker passage or a very opaque passage which usually isn’t until, the last layer or two anyway, for the way I paint, then I might just add a fresh glob of paint.