Essential oils are powerful plant medicine that can be used everyday for lots of different ailments (plus they uplift you with scent!). The four essential oils that I feel it is critical to have on hand: Lavender, Tea Tree, Peppermint and Helichrysum.
Some essential oils can be used straight on the skin, like lavender, but it is best to dilute in a carrier oil like sunflower, almond, safflower, fractionated coconut or oil. Or you can maybe a spray with water.
Lavender is an all purpose wonder. It's a natural antiseptic, analgesic (helps relieves pain), anti-inflammatory and sedative. Rub lavender on your temples (or drop in bath) to calm you down; rub on closed wounds to help them heal; put on a sunburn to help relieve pain and speed up recovery. Mix with water (and peppermint if you wish) to make a protection spray to use when you are traveling to ward off germs and bring calm.
Tea Tree has powerful anti-microbial properties. It is great for blemishes but also good to apply to open wounds to stave off infection. If a wound, bite, cut or scrape looks like it might be getting infected, apply tea tree.
Peppermint is incredibly refreshing and stimulating but also has other benefits. Use peppermint oil to relieve itching (helps with poison oak and ivy); smell or rub on temples to help with nausea, motion sickness, fatigue, or headache; can be diluted and taken internally to help with heartburn and indigestion or rubbed on stomach.
Helichrysum is a healer. It helps heal scars and can be applied to any closed wounds, scrapes or bruises to promote healing.
I like to have all oils on hand in a little pouch that travels with me. If you want to learn more about essential oils, I highly recommend The Encyclopedia of Essential Oils by Julia Lawless.