Hey problems101.
You need the original I-797. I'm wondering why ur employer has it. I took lots of stuff(just incase), but just presented what was listed on US embassy at Nepal site.

-        Approval Notice Form I-797 issued by the USCIS

-        Evidence of Employment in the U.S. (e.g., Job letter, pay stubs etc)

-        Firm Registration Documents(I kept copy of my I-129 instead)

-        Tax documents, if any (w2s)

-        Prior visas/passports

-        Academic records i.e., transcripts

-        Any other relevant documents (i presented leave letter here)

-        Firm registration documents in the U.S. (for L-1) (didn't present this one)

-        Citizenship card

I'm working with a small company too, just few hundreds employees. My friends were working with similar companies, but not sure, why they got stuck. I just got reason  for one of my friend, which I posted earlier.

Anyway goodluck guys