When it comes to describing someone who is intelligent, savvy and quick-witted, there are several synonyms for "smart cookie". For instance, you could describe them as "sharp", "bright", or "astute". Other options include "clever", "brainy", "gifted", "talented", and "ingenious". If you want to emphasize their quick-thinking abilities, you might use "nimble-minded" or "resourceful". Additionally, those who possess a great deal of knowledge and smarts can be referred to as "geniuses", "savants", or "whizzes". No matter which synonym you choose, it's clear that calling someone a "smart cookie" is high praise indeed.