Fitspacks are always a bad idea. If you want something legal to carry, start keeping your keys on a locking carbiner rated for rock climbing. If it has a kilonewton (kN) rating stamped in it, it is suitable. This won’t collapse on your hand and no amount of force any human is capable of generating will break it, but anyone whose nose you drive it into at maximum effort is likely to remember the experience. This should also be legal to carry anywhere.