I would recommend Zach Even-Esh as well. I think he has a 30 day for a dollar trial membership on his site
http://www.undergroundstrengthcoach.com/ The membership comes with a sandbag training pdf.
I filled mine with wood pellets too, with no problems as yet. I have also read that you can get 40# bags of rubber bark like they lay in playgrounds at Lowe's or Home Depot. That you don't have to worry about moisture like the pellets, or if you live in a clime where they don't really sell wood pellets. I know I sweat like crazy doing 10 minutes of 80# get ups that Rob Shaul is a fan of. Be sure to Zip-tie that bad boy though...I had mine explode open after dropping it after one of those grueling 10 mins. I'm still finding those little pellets.
Favorite excercise wise, I like adding in rounds of Cleans in after my weekly Front Squats.