Which one is best for "sand bags" when bench shooting?? I have heard of people using Rice instead of sand??

I use sugar mixed with salt and pepper.

I use the plastic "fill" that you can get at any craft store. Its cheap, waterproof and you don't have to worry about it getting soggy when wet (rice) or leaking (sand).

I use sand as I want the stability of the extra weight.  Rice and other light items do not give me the stability that I like.  The sand I use is the very fine play sand to fill leather rests.  If using something like old money bags, which I have used dozens of, make sure you double stitch the seams and triple stitching won't hurt, and I mean ALL the seams, not just the one open where you put in the sand.  Go over all seams and use the finest stitch per inch your machine will do with the thread you use.  Also, use a heavy thread, not your normal clothing thread.  The thread I use is a black heavy thread #69.  It will not break easily and takes a lot of abuse.  Also, don't overfill the bags, you want them to settle around your firearm forming a cradle.  Then when you are done, just use common since and don't leave them out in the rain.  If they do get wet, set them up in front of a fan for a few days, turning them over ever 6-12 hours.  You will get them dry long before the stitching or bag starts to rot or weaken.

Quoted: I use the plastic "fill" that you can get at any craft store. Its cheap, waterproof and you don't have to worry about it getting soggy when wet (rice) or leaking (sand).

How much did that stuff cost you?

I hooked up with a friend who reloads shotgun shells, and got a healthy handful of shot buffer.  Granular polymer stuff, about the size of a letter "a" in 6-point font.  Works fine.

Walmart sells the plastic beans for beanie babies and dolls.Cheap$!  It works great for a squeeze sock on the rear of stock.

Sand, will not shift as easilly and screw up a shot as other things can.
Jack

Out of desperation, I once used a Horse Feed sack.  I got a ruger 22/45 to hit a 5 gallon bucket at least 6 out of ever 10 shots at 225 yards with a 6-18x 50 tasco scope

Sand would be much better performance wise.  I know nothing of the plastic stuff, and this was the firest time I ever heard of rice.