Bill, I have the 511 push pack and it is VERY close to the same size (I'll try and find a link to what I posted about mine quite some time back). You can pack a 1 lit water bottle, and pretty much anything you would need on a good weather day pack. Actually with my push you can carry two water bottles and still have room for a lot of stuff. The main compartment would probably hold AT LEAST 4 boxes (or more) of 12ga shells, maybe even 6. I wouldn't feel under packed using it for a day bag at all, but ONLY in good weather where other items would be needed. You could even pack a meal and a small fold up stove of some sort (natural fueled) pretty easily.