How to keep the weight off & maintain it?

I recently just reached my weight loss goal by 10 pounds! Woo! I've kept a strict diet & only treating myself to once a week & exercise 30 minutes regularly. But here's the thing. How do I maintain my weight? I don't want to gain it all back. I am going to a buffet next week & how do I deal with this? I'm obviously going to overeat once I see my favorite dishes on sight & I'm currently craving junk food. =( I know I just reached my goal, but am I still able to pig out like last time? I still want to maintain my weight, however. What do I do?! Can I still have my can of soda every once in a while? T.T