The key to the pantry in No Rest for the Wicked

First, the location of the key is shown in the screenshot below. You need to climb the tower in the fortress at the beginning of the game, go outside, go down one set of stairs and walk along the wall (don't go any lower).

There will be a key on this platform:

Go inside the fortress, go to the courtyard with the big fire where there is a door leading to the blacksmith Fillmore. On the right side of the wagon you climb on to raise the gate (with Fillmore's lever), there is a hidden door to a storeroom. Open it and take the reward.