Don't go to a party hungry!
Eat some protein or healthy fat rich food before you go. Nuts, jerky, protein bar, string cheese and fruit, etc. This will prevent you from making bad food decisions because you're not thinking straight. Drink a glass of water for every alcoholic beverage you have.
This keeps you hydrated and will also help to reduce the amount of alcohol you drink. Re-gift food gifts you don't think are going to benefit you.
I know this sounds a little cheap but hey, if you have health and weight loss goals it may save you from blundering. Follow the 3-bite rule.
If you are going to have some tasty treats think morsels. Have 3 bites and be done. You get to try it and hopefully really savor it knowing that three bites are all you get. Who knows you might actually enjoy those three bites more than you would just scarfing down the whole thing. BTW, only choose one or two treats to do this with not five. Take small servings of starchy carbohydrates and large servings of non-starchy carbohydrates.
As we all know most of our holiday foods consist of sugar, flour, corn, potatoes, etc., all starchy carbohydrates. Unfortunately, these foods promote the release of insulin, which causes us to store more fat. Take small spoonful or bite size portions of these foods and load up on non-starchy carbohydrate sources to satiate you. These foods are salads, green beans, spinach dishes, vegetable platters, etc. You may even want to be the person who brings a dish like this to the party so you know it will be available. Bonus Tip:
Remember that alcohol shuts off our inhibitory brain chemicals, which can cause you to say things you might not normally say (whoops!) and eat more than you need to. So Save yourself from this risk and keep alcohol to a minimum. You will feel great in the morning!