Cautions become spent immediately, conditional cautions become spent after 3 months. You only have to declare 'unspent' convictions and only when asked.
It will be filtered from a standard CRB check but not from an enhanced CRB check, so if you are for example going to apply for work as a teacher or healthcare professional then those types of professions tend to do enhanced CRB checks.
In the grand scheme of things I don't think you should worry too much, your caution was for a moment of madness and i think if you do find yourself in a situation where you have to explain it then i imagine most people would see it for what it is, we've all done things we regret when we're drunk.
I managed to work in customer service for various major brands with a caution for possession of Cannabis which i got many years ago.
In my experience if people like you and you make a good first impression then something like a simple caution related to an offense that anyone could potentially find themselves committing, given the right circumstances shouldn't stand in the way.