The best place (within reason) is on the same type of anti static foam that you see chips in all the time. Then put it in a anti static bag or box. Putting the boards in any kind of ordinary plastic or paper/cardboard is bad in a big way. (unless it is treated with special conductive material). When you see plastic think Van der Graah generator 'cause that's what it is.
Make no mistake about it handling these boards in a dry area is reducing their life expectancy. Companies spend 10's if not 100"s of thousands of dollars to protect chips and circuit cards. Where I work we won't let anything that can generate electric static fields come near work surfaces, everything is grounded, Ion generators and humidity control with alarms for everything. We won't even let ordinary screwdrivers near the boards/modules. Static is a killer.
PCBs can be designed to help mitigate static problems and trust me all the arduino boards I've seen are very poorly designed in this manor. It costs money to do it right, power and ground layers for example.
But these boards are cheap and not used for life support (I hope not...) Where I work, anyone who flies depends on our stuff working...
My 0.02$
Kevin