The best advice is Don't Stress. You'll find things to eat. There are always better options.
Thanksgiving - white meat turkey breast, veggies (fresh or cooked, it not prepared with creames, etc)... Turkey is an excellent choice...very low fat if you stick with white meat. I always took raw, fresh veggies with me to family parties and snacked on them throughout the day as people went back for more food. Make a dip to take too if you'd like...16oz container of low fat cottage cheese blended with a hidden vally ranch dip mix packet. It's mostly protein and can make those veggies go down easier. Take an apple with you and slice it, top with cinnamon and sugar and microwave for a minute or so for a yummy dessert.
As far as going out is concerned. Try to choose a restraunt with a varried menu. Going to a bbq place or a soul food place or something specific, it can be harder to find a good option. Almost everywhere will have a chicken breast on the menu. Order it plain and with a side steamed veggies. There are threads with specific menu options at different places around here somewhere.
ALso...drink lots of water. Especially on holidays. I always found if I kept my mouth busy I wasn't tempted to eat more. Drinking water (HNS's too) and chewing sugar free gum always helped me. I bought boxes of sugar free gum at Costco and always had at least two different flavors with me at all times.
Ask questions at your class. They're used to dealing with holidays and eating out and other temptations.

They can be really helpful. Then come back here for more clarification. Some of us have been through many many holidays OP and we'll do it again...and we'll be more than happy to help