The Collaborative International Dictionary of English v.0.48:

Pepsi \Pepsi\ prop. n. [See Pepsi Cola]
   Pepsi Cola; -- a familiar contraction; as, I prefer Pepsi to
   Coke.

   Syn: Pepsi Cola.
        [WordNet 1.5] Pepsi Cola

WordNet (r) 3.0 (2006):

Pepsi
    n 1: Pepsi Cola is a trademarked cola [syn: Pepsi, Pepsi
         Cola]