Bugs!

Many essential oils are natural insect repellents - the ones I use most often for this purpose are citronella and red thyme. You can put a few drops in a spray bottle with some water, and use that to keep insects at bay. I often add a few drops to the water I use to clean the floor.

Be careful with these oils, though, as red thyme is known to cause skin/lung irritation, and you shouldn't use it in a vaporiser or diffuser. Citronella is used in natural insect-repellent candles, but at higher concentrations it's also likely to cause skin/lung irritation - I'm slightly sensitive to citronella, myself, and I can vouch for this! (However, it's useful enough that I use it anyway - but at a low concentration, not more than a couple of drops per 500ml/18oz water.)

These are a few of my favourite oils

My two must-haves are Lavender and Tea Tree.

Unlike most essential oils, these oils are gentle enough to apply neat on most people's skin, which makes them, um, essential items in my first aid kit.

Very briefly:

Lavender is a very soothing, calming oil, and it speeds healing, making it great for burns and cuts (it also has antiseptic/anti-inflammatory properties). A couple of drops on the pillow may help with insomnia.

Tea tree oil is a potent antiviral, antibacterial and antifungal. It's rather medicinal and not as floral as lavender oil, but that can be a distinct advantage if you're trying to apply essential oil to someone who'd rather not smell like a flower shop ;)