I think that you can fu*& up your rotater cuff(cup?) if you use wieghts while striking. Anyone correct me if not. A weight vest would be ok either way.
When you work the bag, move, move move. Work things that you need to tighten up on. To get me used to really exerting myself on the bag, one of my senior students had me throw thai round kicks as fast and hard as I could, alternating legs each kick. After I got my blood pumping I would start working combos. Move. 30 min is ten rnds boxing. If you can go all out with good technique and positioning on a bag, competition beware.
Did I say Move? around and round and ......