When I paint something, I inevitably get interrupted, have to go somewhere, etc. and have to stop and put my paint away. Before I knew this trick, I wasted so many paint supplies. So the trick is when you want to take a break and start up again later you can store your wet paint brush, paint roller, and paint tray in the refrigerator and they will be ready to use when you start painting again. They do not dry out!
Just put everything in plastic. Put the paint brush in a gallon zip lock bag and your roller in a plastic grocery bag. You can put the tray in a large plastic bag or cover it with Saran Wrap.
You can keep the paint brush and roller in the refrigerator for days. If you have paint in the paint tray, you should try to use that by the end of the day.