What is cheap material that absorbs water in packaging?
What you are looking for is most probably silica gel.
http://en.wikipedia.org/wiki/Silica_gel

It is a highly water absorbent material with large surface area. It is often used in packaging as well as in laboratory in desiccators. 

You can actually buy it packed or in bulk easily (let me not link explicit offers here). You can regenerate used (old) silica by heating / drying / pumping, so you don't need to buy every single time new one if the old gets less effective.