What should I fill by wall-bag with?

I have a wal-bag for striking, and would appreciate your suugestions as to how I should fill it. There are three sections, also. Should I use the same filling in all three, or use different fillings?

People I know have suggested dried peas (?!), but I can´t imagine it´d take long to turn them to dust...

 

Dried peas are very good for this, and they do not turn to dust quickly, in fact it takes years.

Under no circumstances should you use sand.

Actually, here's two threads I just dug up about this subject

http://www.martialartsplanet.com/forums/showthread.php?threadid=66564

http://www.martialartsplanet.com/forums/showthread.php?t=35129

 

Thanks! Sorry, I should have guessed there´d be previous topics.

 

iron filings. lol joking.

 

Canned peas take longer.

 

Lupins

 

You couldn't pay me to hit those things. They will knacker your shoulders, never mind your hands. Hit a heavy bag with gloves on.

 

mung beans