What are the literary devices in "An Unstamped Letter in Our Rural Letter Box" by Robert Frost?

Another lovely simile is created when the speaker says,

There I elected to demurBeneath a low-slung juniperThat like a blanket on my chinKept some dew out and some heat in,Yet left me freely face to faceAll night with universal space.

In the simile, the speaker compares the low-slung juniper, under which he decides to sleep, to a blanket that not only helps keep him warm, but also keeps some of the night's dew off of him. Further, in the passage above, there is also an example of personification. When the speaker says that he is left free to be face to face with universal space, he gives space the human quality of having a face. The speaker also personifies his memories when he describes them:

Inside the brainTwo memories that long had lainNow quivered toward each other, lipped Together, and together slipped.

The speaker seems to give these memories the physical ability to lie down, as a person might, the ability to quiver while moving toward one another, and the ability to kiss as they lipped together. Obviously, memories are not tangible objects that can move and shake and kiss, but they sound like two lovers here.
The speaker also employs irony by suggesting that although he is a "tramp," he has experienced many advantages that his "involuntary host" may not have. For one, "sleeping out" has given this homeless speaker the opportunity to witness the spectacular beauties of nature, like the "coalesc[ing]" of two stars in the middle of the night. We would not expect a homeless person to count himself as lucky as, or even luckier than, a person with a nice warm bed in a cozy house, but he does.

The most notable literary devices in Robert Frost’s "An Unstamped Letter in Our Rural Letter Box" are rhyming couplets, similes, and diction.
Frost uses rhyming couplets (two lines of roughly the same length that end in a rhyme) throughout most of the poem.
Frost changes his rhyme scheme for lines 43-47:

43 You have had your advantages.
44 Things must have happened to you, yes,
45 And have occurred to you no doubt,
46 If not indeed from sleeping out,
47 Then from the work you went about

He ends lines 43 and 44 with "advantages" and "yes." This could be considered an imperfect rhyme (words that have a similar sound but not identical sounds). Frost further disrupts his previous pattern of couplets with lines 45, 46 and 47. Instead of a couplet, Frost has three consecutive lines that end in a rhyme.
In lines 7 and 8, Frost uses a simile: "There, pointed like the pip of spades, / The young spruce made a suite of glades." He compares the "young spruce" to "spades."
In line 10, Frost again uses simile: "The place was like a city park." He compares this section of woods to a "city park."
Lastly, Frost’s language choice is highlighted in line 50 when he uses the Latin legal term "forma pauperis."