I found out that good hiking boots are not all you need, spend the extra money on good hiking socks, they make a world of difference,
Ziplock bags have numerous uses,
A poncho is great for covering you and your backpack,
Flipflops for hostels and beaches.
A water bottle with a loop on the lid so it can be tied to your pack,
First aid kit,
Layers of light weight clothing.
A lot of areas that have a lot of hikers will rent you sleeping bags and tents for a reasonable fee.
A sarrong is great for the beach or to through around your shoulders when it gets nippy, also can be used as a towel or to tie stuff up in a bundle.
Twine for clothes line of tying things together or to your pack.
I have a blow up travel pillow which is great for buses, the beach and hostels with rubbish pillows.
A headlight, (you will use it all the time)
Hat, scarf and gloves but you can buy those here at a reasonable price.
A knife, always useful for hiking and camping but also great in the numerous hostels that provide a kitchen but have blunt knifes.
A decent book which will get you started and can be traded with other travelers
A bottle opener.
Its worth buying good hiking trousers as they are lightweight and dry quickly, they are also hard wearing.
Have a great trip