I bleed mopar, Lots of people including some of my fellow Moparites laugh at the notion of weight reduction in fasteners alone only until they see a reduction of 10 pounds in my case alone. I have not even exploited every option just yet cause this is micro weight reduction climate, and it can get expensive.
Of course when attaching important components like doors, hoods, bumpers and a diet is at hand, Titanium should get the nod. Fenders and some brackets can get away with Aluminum fasteners. Some minor and non-important interior items can even get away with super light weight plastic fasteners.
Yes, done and then some. Try special shorten alloy bolts, washers, Lock washers, nuts, machine screws and more.
Here's a flick of my Felix the Cat's magic box attached to this forum way back. This box in itself weighs a combined 3 or so Lbs, so imagine if it were full of steel fasteners.