The easiest way to pass a breathalyzer, of course, is to not land in such a situation. But we can handle this discussion like a hypothetical: What if you needed to pass a breathalyzer test? How do other people pass breathalyzer tests? What are the weaknesses of the breathalyzer device? There are a lot of urban legends about strategies to trick the breathalyzer into a lower blood alcohol content reading and sucking on a penny is just one of them.
The theory is that holding a penny in your mouth (or sucking it, or chewing it, depending on the version of the urban legend) can produce a more favorable breathalyzer reading by basically interfering with your mouth's saliva composition. Some sources say that the more pennies in the mouth, the better, although they must be discreetly discarded before the test. The zinc and copper of the penny (not to mention the grime it's accumulated in circulation) supposedly neutralize or mask the actual level of alcohol by inducing a chemical reaction or coating the inside of the mouth. Some people say the breathalyzer is fooled into giving a lower reading; others suggest the breathalyzer is so confused by this new information that it simply doesn't work.
Regardless of how stealthily this trick is executed, though, it doesn't work. Its usefulness would rely on the breathalyzer device actually somehow measuring the alcohol in a way that it could be altered by other substances. If breathalyzers worked that way, it would be great, but they don't. Breathalyzers provide an infrared light that changes in intensity based on alcohol content in the mouth. First, the breathalyzer's light passes through a sample of the person's breath, which will cause the intensity of the light to change. The change in the light can be used to calculate the amount of alcohol in the sample, and therefore, the person's drunkenness. It's complicated for a little machine, but it was developed specifically because it's hard, if not impossible, to fool. The concept of tricking the breathalyzer test does have a basis in fact, though. Old breathalyzers worked in a way that's similar to how many people seem to assume they still work, by measuring a chemical reaction based on the alcohol in the breath. These results were easier to manipulate with pennies or other tricks.
Other strategies, of various levels of usefulness, include rapid exercise, eating food or drinking coffee, consuming a bunch of breath mints, swishing with mouthwash, faking out the breathalyzer by alternating short and fast breaths or breathing through the nose. It's been a decade or so since any of these shenanigans worked, though.