What is the significance of the ring?
Rashi: The placing of the king's ring on one's finger is a sign that one is second to the king.
What is the significance of the linen garments?
Rashbam: See Yechezkel 27:7. Da'as Zekenim, Hadar Zekenim - The Nile River is called 'Pishon' due to Pishtan (flax) which grew there [in abundance]! Rashi brings so from Bereishis Rabah (16:2. Refer to 2:11:2:2). There, Pishtan is not flax, rather, hemp. Alternatively, it grew in Egypt and was dearer than that of all other lands.
In what merit was Yosef given Pharaoh's ring?
Maharal (Ohr Chadash, p. 129): Because Yosef drew close to Hashem, King of kings, never deviating from Him, he merited close appointment before mortal kings as well.
Why did Pharaoh himself place the ring on Yosef's hand; as opposed to Achashverosh, who handed the ring to Haman, and later to Mordechai to place on their own hands (Esther 3:10; Esther 8:2)?
Oznayim la'Torah: Yosef's hand was rewarded for refusing to touch his mistress. He merited linen garments for leaving his garment in her hands when he fled from the room. 1
Oznayim la'Torah (according to the Midrash Rabah): And so with all his limbs.
Why does it say "Revid ha'Zahav" (with a Hei)?
Ha'amek Davar: It is known - the second to the king wears a gold necklace. The same applies to "Mirkeves ha'Mishneh" in the coming verse.