Which pegs and cords did the b'nei Merari carry?
Rashi: They carried the pegs and cords of the pillars of the Chatzer 1
Rashi: They were placed on top of the pillars in order to attach the hangings to them. According to the Ramban, the pillars did not have pegs. See Beraisa that he cites.
Rashi: They were used to attach the hangings to the ground, to prevent the hangings from flapping in the wind.
As well as the pegs and cords of the Mishkan itself. See Pasuk 26 (Refer also to Bamidbar, 3:26:1:1*).
Ramban: Since the "ve'es Meisreihem ve'es Kol K'lei Avodasam" (in Pasuk 26) refers to the hangings of the Mishkan and the Ohel Mo'ed that are mentioned in Pasuk 25, but not to the Chatzer. See Ramban DH 've'Lo Matzasi'.
See Ramban DH 'Aval'.
Why is there an extra 'Lamed' in "le'Chol Keleihem"?
Rashi: Refer to Beshalach, Sh'mos, 14:28:1:1*.