save the sandbag training for your gyms days. Its very taxing and will interfere with your recovery. Sandbag carries are a great method for conditioning after your lifting at the gym. I’m actually writing an article on different sandbag conditioning methods, if you’d like to read it pm me your email addy and I’ll add you to my mailing list.
I’m not sure about the 100 lb. on the head thing, but I have used smaller sandbags for head carries/balance. It forces you to maintain proper posture and provides some resistance for feeback. It’s impossible to balance the sandbag without keeping the spine straight. The chin must be pulled back. The sandbag has to be positioned on the top of the head and directly over the spine. We walk up and down the stadium steps with 1 on the head and 1 in each hand. Walking lunges in the soft grass are fun (NOT) too,