Get rid of all that black on the flat (with out stetching the texture). That's wasted space in the UVs. I'd model and UV a test real quick as example, but gots to work now.
Although Savage is right that you want to make them as snug as you can, you also want them to keep the same pixel density. So be careful to make sure no one piece is getting a lot more UV space than another. It's fine to give more important parts a little more space when needed (especially if it's something that the player…