Tea Tree Oil.

Probably the most widely available version of Tea Tree Oil is made by Thursday Plantations.

Every naturopathic first-aid kit should contain a bottle of tea tree oil. I really love tea tree oil and think everyone should have a bottle on hand, especially during Summer months which tend to be full of scraps, cuts, dirt, soap-less public bathrooms, camping, car trips, etc.

Product: Tea tree oil is just that, an oil. An essential oil, to be exact. You can buy little bottles of it that can be carried in the car, in a purse, or easily stored in a medicine cabinet or first-aid box. It is not very expensive either: a bottle will cost between $10-15 and will last a long time.

Mechanism: Tea tree is basically a natural antibiotic.  The oil has been shown to be anti-microbial, anti-bacterial, anti-viral, anti-yeast, and anti-fungal. 

Uses: In a nut shell: it is great for sanitizing/sterilizing, cleaning, and preventing infections. It is to be used topically, meaning it can treat infections and/or damage to the skin. I've used tea tree oil when cleaning products (add a couple of drops to soaking water, to mop buckets, when making homemade cleaners, etc). In addition, I've applied it to my skin a bazillion times to treat various conditions and simply as a form of hand-sanitizer when soap was unavailable. You can even add it to your shampoo (especially if making homemade shampoo) and some make homemade mouthwash using a combo of tea tree oil, baking soda, etc.

Warnings: the oil is quite potent and a little goes a long way, so most oil companies advise (on their bottles) that their product be diluted with water or another oil (like olive oil).  So you could pour a bit of olive oil in a dish then add some drops of tea tree oil, mix, then apply to the area needing treatment and/or cleaning.  Another thing to note: the scent of tea tree oil is extremely potent!  It sure smells medicinal :P  Be prepared for the strong herbal smell.  The smell isn't a bad thing, however.  Inhaling small amounts of the stuff (at a distance or diluted with water, try not to directly inhale the stuff) is like providing an anti-microbial treatment for your lungs (good for congestion and respiratory sicknesses like colds/coughs/sinus problems).  Last note: don't eat tea tree oil.  There are tea tree oil-containing mouth washes, toothpastes, and dental flosses, so having it in your mouth should be totally fine, just don't swallow the stuff :P