Every English sentence has to have a subject (except commands), even if the subject is just "it" and doesn't obviously refer to something. "it" in your sentence refers to the situation, his future actions.

The word "it's" is a shortened version of "it is". This is an exception from the standard possessive form of a word. Normally, adding " 's " to the end of a word indicates possession, such as in the phrase "the car's door was damaged in the accident." This literally means "the door of the car was damaged in the accident" However, the " 's " can also mean a contraction of "xxx" and "is." Other forms of this are "he's" ---> "he is ", "he's going to the park now", or "she's back home" --> "she is back home." In this case, "it's straight back to the couch" means "it is straight back to the couch." This means "I go straight back to the couch".

Hi Sonia The 'it' refers to what he will be doing. He will give a talk and then go straight back to sitting on the couch, so 'it' is kind of like his plan. This is not necessarily the correct way to compose the sentence but as in any language, we miss out verbs sometimes.