Fastener material (steel, stainless, zinc, chrome, etc.)?

[IdahoMan]

I'm putting my truck back together (lights, mirrors, grill and drip-rails) and am trying to get the right fasteners.

Looking at the fasteners I removed, some like the DR ones look to be the black kind and a bit rusty, some like the roof light are shiny an non-magnetic (I assume SS). The wheel-well trim screws that are always a bear to remove are magnetic and shiny and look OEM (nickle-plated?).

So I ask: What's the ideal fastener material, and more importantly what reaction will it have to metal it is being screwed into? (Ex: on body sheet metal, I'd much rather the fastener rust than the body)

Secondly: What could/should I dip the fasteners in when re-screwing to help seal out moisture (this is especially important on the DRs), a silicone or Right Stuff?

Thank you!

[Captkaos]

Generally the Drip rails have a gasket on the back sealing the surface from water penetration.  It would be a black glue strip on the back. These are typically black metal screws.  If you want to put a dab of silicone on them I would put it under the screw head.
The roof lights and from what I remember the wheel trim were stainless but I haven't mess with any in a while.
As far as metal reactions you can probably google this but are you looking for something specific from the community?

[Mr Diesel]

Use stainless. I suppose someone somewhere might want to debate metal reactions, but the fact remains that you will have less rust problems by using stainless. I use a dab of grease on threads to prolong the antirust effect, but rust is always looking for a way to creep in. Keeping them dry is single biggest factor, so using that gasket between rail and body is important.