It's relatively easy to export blender materials to a file.
First: UV unwrap the file. If you're using image-based textures, you'll need this to happen already. If not, there are tools to help unwrap, and if you don't particularly care if your end UV wrap is logical, you can use the lightmap-pack uv unwrap to practically eliminate distortion, except that drawing on the image will be a nightmare.
Second: Set the faces to use a texture. Just enter face-select mode (or edit mode, now that the two are combined in the latest version), select all faces. Open a second panel with the UV/Image Editor, and create a new image.
Third: CTRL-ALT-B.
Fourth: Profit!
Most models I've made lately actually rely heavily on this technique. I was able to make the Shiva ammo drum's textures without leaving Blender, and the same goes for the fuel tank. I had to enter GIMP a few times to tweak the paneling and the AO map for the UAV, but other than that the texture was 100% Blender, too.
