You're welcome Dave, not sure if you mean the dome lighting but I guess so. Watch those raytraced shadows they come out way too crisp at default so you should set some light radius to blur the outer edge in a final render and add rays to stop the pixelation. For dome lighting I just want to say one thing because it's important to be aware of, it's a bit of a cheap trick I use it to get quick result and you can't break geometry based light sources. In general for mental ray and indirect illumination your results easily come out very CG render like if you don't have other lights in addition. Something like this will have a huge effect on the outcome of your textures as well, that's why I mention it. Try relighting it without the dome to see how it comes out. You'll just benefit so much from learning how to use direct illumination first it's not too difficult to do and it's crucial both for rendering times and good end results.
For the textures it looks to me like you've got pure black and white materials in there which is why it doesn't come together as a whole. Black absorbs all light and white will completely reflect it which is artificial and would never happen in the real world due to color bleed between materials and multiple colored light sources. If you try to soften those colors a bit to match up with eachother, and also have a crack at lighting the jerry can with spots I think you'll get a much better result. Try to imagine an outdoor scenario where you'd have a directional light with a warm light yellow color as a sun, a few light blue spots as fill from the sky and maybe some low intensity green or brown bounce lights aimed up at the can.
Also the bump on the green material has to come down to a lower value, it is too high at the moment.