HeRO backpacks are sort of ridiculous to add into this equation as there are few in curculation ans if you wernt there THAT DAY you mayswell just stare at them on people's backs, as you aint gettin one unless you pay up the ass.
Also, you cant make a pet carry an item that stacks more then you can hold. If you make a poring hold 900 blue gems they will drop: "Blue gem (900)" and you will never EVER be able to get it back ever again.