Most of the events cost as much or more than a park ticket, not sure if it is cost or crowds that you are looking to avoid. I would imagine most of the events at resorts are sold out already but you could call and ask about cancellations. Lots of resorts have special dinners or parties going on.
The Boardwalk might be a nice place to hang out. They have a few paid parties, but you can also just go. Jellyrolls is open, but will fill up I am sure, it is always a fun time. They open at 7 tonight the website says. You can also walk around to a lot of other resorts and see what is happening too.
It will be a bit chilly tonight, but Ft. Wilderness doesn't seem to have anything special planned this year and might be a nice place to hang out. See the movie and watch the fireworks from the beach.