Sprinkle some salt on your stain.
2. Baking Soda
This might be a little more difficult to come by, but if you have baking soda, you can rest assured that your stain most likely won't be permanent. Start by blotting your coffee stain with a cold, damp paper towel. Then sprinkle some baking soda over the area and let it seep in for a while. Blot it away with a dry towel or cloth - don't panic if the mark is still there. This method will at the very least keep the stain from setting into your clothes. Throw it in the wash as soon as you return home.
There are two things you need to know when treating your coffee stain with vinegar: For one, use white vinegar, and two, beware that your clothes will smell of the substance for the rest of the day. Once you know that, you can start tackling your stain. Vinegar can be included in the clothes washing process, and it's also effective in treating spot stains. Simply pour a drop or two on the stain and blot with a dry paper towel.