I’ve been trying out lots of different solutions to keep my acrylic paints wet both while I’m painting and between sessions and I finally found one that works well for me. Its so simple that it probably doesn’t need its own thread but here it is 
Supplies: 2 small cookie sheets, wax paper, paper towels, spray bottle with distilled water, and optional clips
Step one - place the paper towels in the cookie sheet and spray with distilled water until saturated but not sopping wet
Step two - place a piece of wax paper on top of the paper towels
Step three - enjoy your new stay wet palette!
For storage I put the second cookie sheet on top and clip it with these little clips from the hardware store. The clips are optional, I use them so I can move the palette around.
I’ve been using this setup for weeks and it’s kept my paints in perfect condition. When I go to paint for the day I gently lift up the corners of the wax paper and see if the paper towels could use a few more sprays of distilled water. While I’m painting I give my paints a little spray, maybe once an hour, and before I put the lid on for the day.
Here’s my two week old palette still going strong. You’ll notice that not only are the paints themselves still wet but most of the mixes stay wet for days as well.
As a secondary option I’ve been playing around with storing my more fluid paints in these little condiment cups and storing them in a plastic bin. The paints do get contaminated this way. I keep a wet paper towel in the plastic bin and replace the condiment cup lids when I’m done painting.
Then I just use the stay wet palette for mixing
Thanks for looking! This was my first tutorial, I hope it was helpful