How can i prevent diabeties?

ok, my mom just got diagnosed with it which is kind of ironic cause she was always talking about watching her blood sugar.my grandma on my dads side has it as well.is this hereditary or no?can i prevent it?im skinny and i have a fast metabolism, so i tend to eat a lot of sweet stuff when im stressed, angry or even bored which is a bad habit.how can i change that?any tips on what to pack for lunch, when/what i should eat for snacks?im lazy, so nothing too time consuming to make =]