Many things lumped under common knowledge aren’t, in ShadowRun they had developed the idea of giving a bunch of bonus points to represent hobbies and secondary areas of interest. This is not required in Savage worlds, each player should come up with 4-6 areas of expertise representing interests, hobbies, etc, that are covered by the characters common knowledge rolls. Examples are abundant in most later SR rulebooks, with things like Urban Brawl, Gang Identification, and Elven Wines being typical.
The etiquette most appropriate to your upbringing is also included in this category, so if you grew up in a corporate burbclave you would have corp etiquette as a part of your common knowledge.
Common knowledge rolls are generally at a higher difficulty than other skill rolls, so it is still likely worth buying etiquette should you actually want to be good at talking to people.
Because of this it is good to come up with a rich backstory, it’s a lot cheaper than buying lots of skills.
Etiquette replaces streetwise and persuasion, and functions in a similar manner to both, in the correct environment. There are many etiquette specialties, and you can have at most 1 per step in the skill (1 at d4, 2 at d6 etc.). Common specialties are street, corporate, high society, tribal, etc.. Rolls made without a given specialty are either defaulted or handled under common knowledge.
Contacts is treated like a skill in this game. Everyone starts with a d4 (unless they take a hindrance to the contrary). Contacts is not linked to an attribute and can always be raised at the less than linked attribute cost.
You get named contacts equal to ½ your skill level (2 at d4, 3 at d6 etc.). A contacts roll (modified by cheddar, aka, bribes) determines how helpful an appropriate named contact is willing to be. You also can beat the bushes; look for friends of friends etc. with a contacts roll. Contacts skill rolls are modified by charisma. Characters with the charismatic edge get an additional named contact.
All characters can speak a number of languages up to half their smarts -1 for free. The linguistics skill adds a language per rank.