It's hard to beat a really good traditional champagne cocktail, which of course has the advantage that you don't need to bring all that extra equipment with you, just a sugar cube, and that magic little bottle of bitters! The Red Room Bar at the Hong Kong Club does the best I have encountered so far, but I am very willing to try others ;-)

Having said that, if champagne cocktails are your thing, you should try CX's signature version, invented by a barman at the Hong Kong Jockey Club. It's fabulous, and rather wicked too (don't have too many!). Here's the recipe:
Put ½ oz. Drambuie into a champagne flute
Top up with (good) champagne
Add 4 pieces each of lemon and orange zest (very thin slivers - think "julienne" style)

My mouth is watering now :-P