So if ya want to load up the pack and get some excercise in, what do you use for weight? I really don't feel like unpacking all my usual backpacking gear to load on the pack. Need something more practical. I've tried all the usual rocks, dumbells, even a 6 gallon water jug, but nothing really duplicates the feel of a hunting pack. There has to be a better way. What do you guys use?