How much contribution does this have on formation of cavities?: not brushing teeth one night after drinking coke

None: Sugary drinks like coke, that do not linger in the oral cavity, especially on one occasion will have no clinical effect on cavities. Sugar, in lingering contact with oral bacteria on a continual basis would be cause for cavities. It is the bacteria, who eat the sugar and then produce as waste acid, eat at enamel are the cause of cavities. Brush and rinse well after all carbohydrate intake!

Verry little: This one night stand won't cause any problems but many can since coke has a large amount of sugar present.If anyhing rinse a few times to reduce the sugar content.

Plaque Free: Mouth in a routinely maintained balanced ph should not be affected with one night of failing to brush teeth after drinking soda. If the environment is reversed, (high acid with existing demineralization on a structure due to presence of plaque formed by microorganism and further drenched in sugar), may trigger the last straw to the finish line to disintegrate what is already a weakened.

Hard to quantify: You've asked a difficult question to answer. If this was the only time and you are rigorous about your oral hygiene under normal circumstances, than the additional risk was minute. If on the other hand this is a repeated pattern, than you're at a higher degree of risk. Regardless, it sounds like you already know the appropriate behavior! be tough and stick with the program!