Eat before leaving for brunch
You need hangover food desperately, but the wait for New Year's Day brunch will make the waiting room at the doctor's office seem like a NASCAR track. Maybe try a new category on Seamless, like "kosher vegetarian," which actually exists. You'll probably be hungry again by the time you sit down, and even if you're not, you should probably eat anyway because, as with all your other pledges, you're not going to kick off "only eat when I'm hungry" 'til Monday.
Don't feel ashamed of what you did last night
Even if it involved someone you see at brunch! Shame will only suppress the endorphins you desperately need to kick in in order not to feel like a building has fallen on your head. Hopefully you've achieved a level of maturity that allows you to feel comfortable with all of the shameful things you've done anyway. And if you didn’t do anything shameful last night, you should be ashamed of yourself.