For those of us that had the knapsack disappear after summoning Aquementas (and weren't smart enough to read the previous posts about emptying EVERYTHING OUT OF IT FIRST, just like I didn't), you simply need to recollect 11 silvery paws and the irontree heart.  The totem required appears in your inventory after you slay Aquementas.  Oh well.  Thanks to everyone else who posted the helpful info. Enjoy...