I put aside the "legal" question point out some considerations:
1. don't buy anything that you would not cry over if some authority simply took it from you for the h--l of it or you lose when someone steals your backpack.
2. there are pluses and minuses on a SAK. I recommend the Huntsman model, used from eBay. You are more likely to use an SAK model with a pair or scissors, tooth pick and tweezers than a heavily encumbered model. You said put in a back pack.
3. when I go on a college campus with my rolling suitcase of books, the suitcase includes Spyderco Police model and an extra pair of reading glasses. It doesn't replace my carry knife on me. It is for the rare (happened on the campus I go to) active shooter situation.
There are good points here except
PLEASE do not get misconceptions about the effectiveness of a folding knife in an active shooter scenario.
Folding knives are already pretty terrible as far as defensive tools go. Folding knives kept off-body in bags, suitcases, etc. are even worse. Situations with active shooters are a bad subset of possible defensive encounters in which a gun is already in play. Luckily, they are also
extremely rare as far as defensive encounters go. They have a disproportionately large footprint in the public mind because they get huge media coverage and are then continuously "reposted" in public discourse by politicians, activists, and well-funded anti-gun groups. It does happen. Just understand that in the extremely rare case that you are on scene when it does, it will be just as rare that the circumstances will be right for your pocket knife to make a difference (besides getting you killed).
The point is that if this is a serious factor in your EDC desicion-making, then you need to take it seriously enough to seek an appropriately effective solution. While a fixed blade is better than a folding knife, and on-body is better than off-body, it's still orders of magnitude less effective than a firearm.