I use 'bake' to turn everything into a single texture.
First you have to go to 'UV Maps' and create a new UV. I used the name 'UVBake', but it can be anything.
Now select the entire mesh, press the 'U' and 'Unwrap' key.
Now in the 'UV Image editor' create a new image.
Now in the rendering panel, go to 'Bake' and select 'Textures'.
Click on 'Bake' and you will get all the textures in a single image. Save it.
Now you can delete all the materials that belonged to your object, and create a new material.
Create a new texture and select the one you made. ////////////////////
If you did everything right, you'll get the same result in just a single texture.
Now simply export your object the way you prefer.