Are there new hats to be revealed during this Winter Bash? I remember that this was done in some earlier Winter Bash. This Winter Bash already feels a bit exhausted: all accessible hats are collected, and only extraordinary activity or extraordinary luck will bring in some more of them. Some new wood to lit the fire would be a good thing.
We might get a Christmas hat, like the last three years. I say might because we had a December 21st hat the last two years, but it doesn't seem to be the case this year; otherwise, they'd already been awarded.
Otherwise, the only thing we can do is act like we normally do; all hats are designed to be earned while contributing (positively) to the Stack Exchange sites, not doing 'stupid' things like posting 15 comments on a Q&A thread. Oh, wait ...
Most likely, all the hats are earnable at this point. There may still be some undiscovered secret tags that someone will eventually stumble upon, but if that's the case, it's unlikely that we can't earn them yet. The only thing we can do to find them is act like normal (or maybe a little bit weirder than normal) and hope that another one turns up.