This is a very very interesting card. It's utility isn't very apparent on first glance. In terms of straight value, Backpack is only ok. It costs an action, a card, and 2 resources in order to draw 3 cards. So basically you've spent an action and two resources to get 2 additional cards. That's not great value.
Where backpack becomes much better is if those cards that you draw synergize with each other. For example, if you're using a Jim deck with Grotesque Statue, Ritual Candles and Chthonian Stone, Backpack will increase the chances that you can have all three cards out at the same time. That is very valuable.
So look to put Backpack in item heavy decks in which the items themselves combo with each other. If the items do not have synergy with each other, I don't think Backpack is very good in terms of straight value.