The phrase "gat in on act" means to get involved in a situation, typically in a sneaky or opportunistic way. There are several synonyms for this phrase such as 'jump on the bandwagon', 'take advantage of a situation', or 'seize an opportunity'. Other synonyms include 'get in on the ground floor', which suggests getting in at the beginning of something new, or 'capitalize on', which means to make the most of an opportunity for personal gain. 'Join the fray' is another phrase that implies jumping into a situation with fervor or enthusiasm. Whatever the phrase, these synonyms all suggest a certain level of cunning and opportunism when it comes to taking advantage of a situation.