You may have noticed that you have a clear space at the bottom of your texture. This is where you're now going to arrange some more textures, namely the wood ends of the pallet. The reasons for putting them on the same texture are:
Ease of use when modeling
Economical on file size (using all of the memory block allocated to the texture)
Better in game graphics performance
You don't need to work on multiple files when resizing or changing color or shade
Easier to bundle with the asset
I'm sure there are many more you can think of too. If nothing else, this keeps everything neat and tidy. If you end up with a game level with 500 assets in it, do you prefer 500 textures to go with it, or 5000? Things can get messy very quickly. So, on behalf of your future employer, I counsel you to texture in this way! Here's an example from the Bootcamp Demo level-bundled with Unity 3D. It's a 1024x1024 size image, and as you can see, every available space is used so...