Prem has the solution:
The "obscure fellows" are the nine members of the Fellowship of the Ring in JRR Tolkien's Lord of the Rings.
I think some of the explanations are not quite right, however. The lines of the riddle are cryptic clues.
An apple for Charlemagne,
PIPPIN: double definition; one of several types of apple and the eldest son of Charlemagne. ✻
one that takes great steps,
STRIDER: simple definition. Strider is Aragorn's nickname, used on his first encounter with the Hobbits
returning in Skyrim or Oblivion,
BOROMIR: hidden backwards in skyRIM OR OBlivion.
and flag unfurled.
GANDALF: anagram ("unfurled") of AND FLAG. ✻
Dave's mentor, venerable sage,
SAMWISE: SAM (or Samuel, who is King David's mentor in the Old Testament) plus WISE (venerable sage). I didn't get the OT reference, so many thanks to dennisdeems for the explanation in the coments below. ✻
in high spirits!
MERRY: simple definition. ✻
That way the celebration.
FRODO: "To and FRO" is this way and that way and a DO is a party. (✻)
Most of sweet lime drink coming to me;
GIMLI: Most of GIMLet (sweet lime drink) plus I (me). ✻
go sell a pretzel??
LEGOLAS: Anagram ("pretzel") of GO SELL A.
The answers marked with ✻ have already been given by Prem, although not necessarily with the same or full explanation.