If you can only afford a few essential oils then the following oils can be used in a number of ways and should be the basis of your essential oil 1st aid kit:
Tea Tree
Tea tree oil is distilled from the leaves of the Melaleuca alternifolio or tea tree which is native to Australia. The oil has been used for centuries as a traditional herbal remedy for skin conditions including fungal infections, spots and dandruff. The oil is antimicrobial and has antibacterial, antiviral and antifungal properties. The smell of tea tree is camphorus, 'green' and fresh.
As with all essential oils, tea tree oil should be diluted for use before being used topically.
Lavender
Lavandula augustifolia essential oils is extracted by steam distillation from the buds of the lavender plant. It is a highly versatile oil and can be used for relaxation, to treat burns and infection, relieve anxiety and calm sensitive skin. Lavender is one of the first essential oils that was noted for its efficacy by Gattefosse, a French chemist who is known as the Father of Aromatherapy. He had badly burned his hand during an experiment in his lab and thrust his hand into the nearest vat of liquid which happened to be lavender essential oil. He was astounded at the reduction in pain and how quickly his hand healed.
Lavender oil can be used topically and blends well with other flower oils in a base oil or cream. It can be used to aid relaxation via steam distillation or in a diffuser or burner. If you add a few drops to the cardboard tube in the middle of a toilet roll, you can use it to freshen your bathroom.
Eucalyptus
Another native of Australia, Eucalyptus essential oil is steam distilled from the leaves of the Eucalyptus tree. The oil is traditionally used to help ease congestion and is especially useful in steam inhalations to treat colds. The scent is strong, sharp and green. Eucalyptus oil should never be used directly on the skin and must always be diluted into a carrier oil before being used on the skin. It is a useful addition to a muscle relief blend and can boost circulation.
Lemon
Lemon essential oil is extracted from the peel of the fruit which, when diluted in carrier oil can be used topically on the skin to treat exhaustion, kill viruses and bacteria. Care must be taken not to use lemon essential oil on skin that will be out in the sun as it can make skin more photosensitive. Lemon oil is a lovely oil to use in a diffuser if you are feeling ill - it can help to purify the air and improve your mood. It really is a sunshine oil!
Peppermint
Peppermint essential oil is extracted by steam distillation from the whole of the 'above the ground' part of the peppermint aromatic herb plant. The oil has a sharp, bright and cooling aroma and is helpful in reducing congestion and headaches. It is effective in helping to ease stomach cramps and easing nausea. Peppermint should always be diluted in a carrier before being applied to the skin. It can also be diffused to help freshen the air and combines well with lemon to ease congestion. If you combine it with eucalyptus it makes a very effective muscle relaxant.