Thanks guys ! This is good stuff. I had no idea what to fill my sand bags with, other than real sand. I thought baking soda, salt, anything inexpensive, not too heavy, and won't clump.
The airsoft BB's is a great idea ! I was also thinking silica gel. Crushed walnut shells like used in sand blasters like Widget23 said is also a great idea.
I think I'll go to Big-5 soon and get some airsoft BB's. Seems like the best overall idea. Won't smell, clump, leak, etc.