I recommend getting a few generics and going to one of the games. Sometimes there are no-shows and if so, they allow those with generics to fill the slots. (You would actually be surprised at how often this happens at conventions as many people overbook themselves and then remember they have to eat/sleep/etc. and are too worn out to attend events they paid for.) Some GMs have a couple extra spots per table reserved for those with generics. For example, if a D&D game has a table maximum of 7 for Adventurers League, the event host may only post 6 seats available for signups and have one spot for 1 additional seat for someone holding generics (coordinated through the Gen Con events team).
Some of the games also have space around the tables for people to observe (though there are very few places during Gen Con that have extra room for this, it does happen occasionally).
Your post stated you got a few tickets to the CoC games, and if that is true, even though they are sold out now, your spot is already reserved. If you meant to say "I was intending on getting a few tickets to CoC games"... then generics are the way to go!