My Bergil calls Pippin "Sir Pippin"--a special nickname for him from Bergil, though he uses "Sir Peregrin" if they are both on duty. I would think "Master Samwise", and probably "Sir Meriadoc". Frodo he would probably call "Ringbearer" until Frodo objected, and then either "Master Frodo" or "Master Baggins". Merry and Sam might be able to persuade him to be a bit less formal in private, and I know Pippin could, but I can't imagine him getting over his awe enough to address Frodo without an honorific.

I really liked this little chapter: Frodo objecting to the cold cloth because he's afraid of Aragorn putting on his healer hat, LOL! And his knowledge that Sam will probably do anything *but* rest. Bergil's offer is so natural and perfectly in keeping with his character. I think of him as a rather solemn responsible lad most of the time, who takes his duties seriously.