You can fix scratches with felt pens and crayons quite nicely. Just match the colors, or blend two colors together. Crayons are great because you can actually fill in scars with them.
To give bare wooden furniture a shiny, polished look, heat cooking oil until it smokes, let it cool and rub it in with a soft cloth. Olive oil works best.
Use baking soda works to remove recent water marks.