There are many shops hidden around the kingdom of Hyrule. Some of these shops have some very good items that you may want to snag on your journey.
Requirement: Red or Blue Candle for cheapest price, 90-160 rupees.
There are a couple of places where you can buy this, but the cheapest place to buy it is well hidden. From the start screen, head right one screen, up three screens, and left two screens. Burn the top left tree on this screen to reveal a staircase leading to a shop that sells the Magical Shield for 90 rupees.
Requirements: 250 rupees.
You definitely want this item as early as possible because it reduced damaged by 50%. From the start screen head up one screen, left three screens, and up three screens to find two rows of Armos statues. Touch the middle statue in the top row to make it move and reveal a stairwell leading to a secret shop. Buy the Blue Ring here for 250 rupees.