We have been using a cocktail of CK-CAM5.2 and CK-AE1&AE3 for years.  As usual, the optimal concentrations of the components will depend on your fixation/processing, antibody incubation time, detection system, chromogen, etc.  My experience with making antibody cocktails is as follows:  titrate each antibody in the cocktail to its optimal concentration then, when preparing the cocktail, use 50% (half) of what you would normally use.  I have found it necessary to do this because when antibodies are used in combination there is an "amplification" that occurs that results in "over-stained" slides in most cases.

For example:

If you use CK-CAM5.2 at 1:100 and CK-AE1&AE3 at 1:1,000, you would  prepare the cocktail so that the CAM5.2 dilution is 1:200 and the AE1&AE3 dilution is 1:2000.  We dilute our primary antibodies in PBS with 1.0 % BSA and 0.1% sodium azide.  Obviously, some "fine-tuning" of the concentrations may be needed.

R. Cartun