Take a wander down to the less-visited, far end of Diagon Alley. Here you will be rewarded with a wide variety of items essential for any wizard - unicorn horns, vampire fangs, rat's tails, mandrake roots....
For the busy wizard, a variety of pre-mixed potions are available also. Please, one bottle per customer.
You are looking for a large sistema container. The stock is located behind the shopfront. Please ensure the container is re-hidden well.
The easiest access to the cache is along the track past the Owl Mail caches. This will give you a pleasant, almost completely flat 2km walk to the cache.