This is not my idea, I'm sure everyone knows about it or something similar however I figured I would post for those who might not.

U.S. Walmart Prices:

$14 for 1 container of 10,000 airsoft BB's
$3 for 3 pair of crew socks (you get to keep 2 pairs)

Very light, surprisingly stable, and a media that is not sensitive to the elements.

I put about 60-70% in one, the rest in the other. Gives you two different size bags for whatever you're shooting at. Pick it down, twist it up, and tie a knot. Similar to a loaf of bread. Then just fold the sock back over and you're done.