First Aid Kit
Remember that you will be in a First World country with more Farmacias than bottle stores! The pharmacists along the camino are quite accustomed to most of the aches, pains and ills of peregrinos and will be able to help you with most maladies.
Take any prescribed medication with you but only small quantities of other things as you can top up along the way.
If you are, or ever have been, allergic to anything - whether it be flora or food - carry anithistamines. Non-drowsy for the day and drowsy for night (so that you can sleep through the snoring!)
If you have ever had asthma - even if you haven't had an attack for 10 years - take something with you. Your body has learned to fight local conditions but you will be in a new country with different dust, pollens etc and these could cause problems.
Build up your reserves of Magnesium and Calcium before you go. Just as you would service your car before a long journey, your body will need a good top up too! (Dolomite is a good source.)
Take pills etc out of the boxes and pack them into plastic, zip-lock money bags. You can decant liquids such as Arnica oil from their heavy glass bottles into smaller, plastic bottles. (They will remain stable for the short time you are walking on the camino.)
If you are walking with a friend, share the first aid list. One can carry the pills for whoopsing, the other for poopsing etc!
And, please, take a plastic packet for toilet tissues and discard in a bin - not on the path.
Pilgrim hugs,
Sil