As I'm sure you know, acrylics dry quickly. Sometimes too quickly. Your half hour break for lunch will find a palette full of unusable dry paint when you return. A simple box (I built mine with a clear acrylic top) will keep your paints wet even overnight. Just give the top of the lid as well as the paints a squirt of water from a spray bottle when covering your paints.
Another commercial method to keep paints wet is to purchase "Masterson's Sta-Wet Palette". With this you use the wet sponge and a special paper palette. It will keep acrylic paints very wet for many days.