We grow Lavender in our yard. It can be used in herb form, but is most often distilled into an essential oil. Essential oils are great for many things. If you had to pick one for preparedness and storage, pick LAVENDER. It is reasonably priced, readily available and keeps quite a while in storage, especially if kept in sealed bottles and away from heat and light.
Unlike most essential oils, lavender can be applied undiluted (termed "neat") for first aid purposes. Used to treat insect bites, sunburn and nettle stings.
It may be used alone or in combination with most other oils. Essential oils are best diffused or inhaled, but can be generally applied with a carrier oil such as olive or coconut to massage into the skin.
A century ago almost every cologne contained lavender oil. Today it is being rediscovered by a new generation learning to bask in its multiple benefits. It benefits so many of the body's systems. It is antiseptic and uplifting to the emotions.
Can also be used as a deodorant when added to olive or coconut oil.
I recommend a 1/2 oz. or 15 ml. bottle for storage purposes. Rotate, if possible.
It can be ordered from several different places. One of my favorites is Nature's Gift. Many MLMs carry oils, such as lavender. They are usually high quality, but also carry a much higher price tag and would have you believe theirs is the "best".
I get mine directly from the wholesaler.
I also have some in stock for around $14 a bottle.