Question about 2 objects in 4x11 -- no spoilers from my question

I don't know whether any replies will contain spoilers, so if you're spoiler-averse, please proceed with caution.

At 18:46 in my version, Sarah is on (or at the edge of) Roy's property and she opens the door of what I assume is the mailbox for Roy's property -- it's wooden, on legs (presumably to keep out critters and to keep it the right level for the mail carrier), has a slanted corrugated metal roof (presumably to keep the inside dry), and is larger than 45cm x 45cm x 45cm [at least 18" x 18" x 18"] (presumably to accommodate large parcels, because isolated homes might purchase a fair amount of mail-order goods).

1. Is this a typical mailbox for a rural property of that era? If it isn't primarily a mailbox, what other uses would it serve?
2. Sarah removes an enamel pitcher from its interior. Why would someone keep a pitcher within -- to provide water for the mail carrier on a long route? For other reasons?

Thank you, anyone who can shed light on this.

"All you need to start an asylum is an empty room and the right kind of people."