Those are installation bolts for a hood or microwave to be used if there are no structural supports to hold the appliance in place. The appliace came with regular bolts as well which would be the first choice if possible. The big washers are used to hold the appliance up against an upper cabinet, again only if it was needed. They are leftovers, you can discard them.
The rectangular part is a vent duct baffle. If your microwave has a vent built in, and vents to the outside, then you use this to prevent air from coming in through the vent. The same is true for your range hood, so it would be used on one or the other, whichever is over the cooktop and vents to the outside. If your vent has a baffle built into the exterior cap, a rectangular piece you will see outside the trailer above your cooktop, then this baffle would not be used. Again, probably leftover part they didn't need to leave for you to puzzle over.
The last bag I can't tell what is inside, but more than likely the same issue. I have installed many of these appliances and leaving the spare parts around causes confusion so bad move on Keystone's part, but in their defense, they hire unqualified/ inexperienced workers so what can you expect. Can't get good help these days...