Dr. Yoshi's attire isn't very different from his normal outfit, as he simply has a pack with a strap around his shoulder. The pack is gray and has a Megavitamin symbol on it; because of this, he presumably keeps Megavitamins in it.
Dr. Mario World
Dr. Yoshi's first canon appearance is in the mobile title Dr. Mario World, where he is an unlockable playable character. His special ability has him select three random locations before clearing them of objects; his animation shows apples falling on the locations before he eats then.