We put in the backpacks so you could organize your inventory a bit better. Put stuff in there like keys, or stuff you want to keep till later, or stuff you want to sell.
I don't understand the crates thing. Do the backpacks weigh too much?
We can do that exactly with crates that we pick up and put in the inventory. Crates weigh 5, bags weight 1, which doesn't make any gameplay difference, really.
Although bags are neat, they are useless so far.
Make crates (baskets, and so on) not possible to put in inventory, and people will crave for bags.