I hacked into my demo Activity, which is a cluttered mess that i'm using for internal testings of all kind. So i can't post the complete Activity here, but all i added was this (it's called rock because it replaced an object that was already there):
Texture woody = new Texture(res.openRawResource(R.raw.wood));
TextureManager.getInstance().addTexture("wood", woody);
Object3D rock = Object3D.mergeAll(Loader.loadOBJ(res.openRawResource(R.raw.boxobj), res.openRawResource(R.raw.boxmtl), 0.1f));
rock.setTexture("wood");
world.addObject(rock);
...
world.buildAllObjects();