"As If": This was added to the FAQ (v.1.7, March 2020) and then amended (v.1.8, October 2020). You can read the October ruling on the ArkhamDB rules page here. (I'm adding a hyperlink rather than retyping the rules in case in future the ruling is changed or amended - at that point, the rules page will be updated and all ArkhamDB FAQ entries will link to the correct ruling.)
Q: Can I look at facedown cards beneath or attached to other cards I control? If I use the ability on Ancestral Knowledge to draw one of the cards attached to it, am I allowed to know what each card is, or is it random? A: Unless an effect states otherwise, investigators are allowed to look at the other sides of facedown cards beneath or attached to cards they control, such as Ancestral Knowledge, Backpack, and Diana Stanley. If you are given the ability to draw, play, or interact with one of those cards, you may look at them to know which one you wish to draw or play. This is not true for facedown cards that are attached to encounter cards or placed facedown via a scenario effect, such as swarm cards, empty space, or tomes beneath locations in the challenge scenario Read or Die. In these instances, players cannot look at the other side of those cards unless instructed otherwise. - FAQ, v.1.9, June 2021
After trying this card a bit i'm actually very impressed.
This is a hybrid sort of card, it's a Tutor that actually searches for cards in bulk. That makes Backpack a weird sort of cross between Preposterous Sketches and Prepared for the Worst. So, what exactly does it do?
First off, this is a tutor effect. If you have powerful items or supply cards like Lightning Gun, Key of Ys, Strange Solution or The Gold Pocket Watch then this thing greatly hastens the rate at which you get them in play. This effect can be absolutely worth it even if you have only a moderate number of targets in your deck overall.
Second, this is a "bulk" tutor, it doesn't just hit some small and limited pool of key cards, it hits a variety of helpful cards like Emergency Cache, Knife and Flashlight, this has the double effect of A: drawing cards and thus shrinking your deck. B: Getting chaff and gunk out of your deck, thus shrinking it. The latter effect is actually better than it sounds, often you're looking to draw an important event or asset (Rite of Seeking for example or "I've got a plan!") and getting all your Flashlights and Emergency Caches out of the way can be invaluable, especially since these cards don't occupy hand space and thus don't mess with you when you're drawing aggressively.
Third, if you're looking for particular cards (as is usually the case when you slot tutors), even if you don't hit all three cards it is still probably a decent play. If you hit just one card, if that card is something like Lightning Gun, then it was still probably a fine play. If you don't draw the thing you're looking for, or nothing at all! then it was still probably a good play because at least the deck is shuffled, thus your chance of drawing the thing you need quickly is refreshed. In other words: Either you get what you wanted or you get a "re-roll" on the odds of drawing it soon.
So, how many items/supplies do you need to warrant backpack?
I've tried some item heavy dudes like William Yorick and folks with just normal item amounts. Generally I lend higher priority to backpack when there's upgraded targets in the mix. As a rule I found that hitting just 2 targets is perfectly acceptable.
8-9 viable targets is the absolute minimum and I'dd only recommend it if there's cards in there like Key of Ys, Strange Solution or The Gold Pocket Watch that are really powerful and can't be tutored with Prepared for the Worst for some reason.
So... this card reminds me very much of Preposterous Sketches, a card that is honestly pretty mediocre. The simple reality is that paying 2 resources and an action to draw three cards isn't economically viable in a game that is essentially about action management.
However, this card has
one two major upsides over Sketches. The first one is that it cannot find weaknesses. This is actually a bigger deal than it seems at first glance since weaknesses are a major reason not to aggressively draw cards.
The second reason is the selection. You don't play backpack in any deck, you play it in a deck that has multiple Item or Supply cards that you really need. Here is a list of all Item and Supply cards.
While it could hit Emergency Cache (and is probably nice if it does hit at least one), you are really looking for decks that run a large number of qualifying cards. Mathematically, you want half your deck to be Item/Supply cards (probably more so you don't miss). Because that's the problem with this card: if you don't get three cards under it, it's really quite mediocre.
However, because it also takes up a body slot (not the most contested, but not trivial either), I don't see this card getting a ton of play. So, better than Sketches in a few decks, but probably still not the Diesel we need.
- Along with Calling in Favors, the second neutral "tutor" type of card, so it can be added to any investigator's deck.
- Cards below this one don't count toward your handsize.
- Cards below this can be played with stuff like Ever Vigilant
- Treacheries like "discard X cards from your hand" won't affect this one
- Thins out your deck. You don't have to play the cards below this one
- Can be recovered with Scavenging to be played again and again...
- Very useful to search for specific cards, like signature stuff with matching types (Zoey's Cross, Finn's Trusty .38,...)
- Can "find" a second copy of itself, which can be played as normal. Be aware that this discards the first copy and you may lose other cards below it.
- Play this card with William Yorick and discard it while 3 assets are below it (for ex. by playing another body slot item) to get more assets into your own discard pile to make more use of his special ability
- Cards below this cannot be commited
- Treacheries that discard this one put all assets under it into your discard pile as well
- It's effect can be wasted a bit, if only 1 or 2 cards were found
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.