I needed to see some more posters. The book Graphic Poster Annual 08/09 had a couple of posters. The Falstaff poster by Yann Legendre fitted the brief in terms of its three colous and simplicity. I found the other posters in a similar style on the Yann Legendre website.
I also liked the simplicity of the HP advertisement by Goodby, Silverstein & Partners
I liked the aspect of the photograph these pint glasses.
I considered different bottles and glasses to represent alcohol. In the UK I think the most representative of a pint is a simple pint glass above.