I have Dragonskin Tactical outfit and Gasmask but when I wear them they change textures like every two seconds. It's kind of annoying, does anyone know how to fix it? And how do I fix the red exclamation mark?

Open up Fallout Mod Manager and click the button on the right side that says Toggle Invalidation. Will work now

That actually didn't work.

Could someone else please reply? I would like to use my downloaded items without looking at the constant hideous retexturing.

Either it's Invalidation issue or you didn't install textures that came with the mod.

Can't find a file for textures on a few..

Read the download page that you got the trouble mods from, and see if they require you to download either the original mod (cause maybe it is an edited version) or another mod. Some mods require you to have one or more other mods in order for the mod to work.

It didn't say any requirements, all requirements were optional. I can't find the texture files in my documents, may be the issue..