The "May Contained" Situation

Restaurants:
When you ask restaurants or bakeries if the food you're buying contains whatever you're allergic to, a common answer you will get is: "We can't guarantee anything because there might be cross-contamination / they were made near each other." Now, this might make you want to back off and give up purchasing the food. But I'd eat the food anyway. Why? The chance of it actually containing the things I'm allergic to is extremely low. The cooks are required to say that because they don't want to be blamed if something actually happens. 
I still need to be prepared, but I want to eat in restaurants like everyone else.

Even so, I can't guarantee you anything. This is just what I do. If I want to eat a brownie that doesn't have nuts in its ingredients but was made in the same kitchen as nuts, I'll eat it. 
HOWEVER, if the person selling the food doesn't know for sure if it contains the thing you're allergic to, DON'T TAKE THE CHANCE. Too many times I've eaten a home-baked good after the baker told me he/she was "pretty sure" there weren't any nuts...this was false and I suffered as a result. Make sure the person talks to the chef or reads the ingredients. Even if an innocent mom brings in cookies or candy, make sure she's read the ingredients on the package.



Buying packaged food:
Often, when you read the ingredients to packaged food you'll see a "may contain" list. Similar to my restaurant explanation, the companies don't want to get in trouble if any cross-contamination occurs. Having an allergic reaction to something on the "may contain" list is very unlikely. 
I'm in love with chocolate, and many of my favorite candies have nuts on their "may contain list." It seems silly to give up my Crunch and Hershey's just because they were made in the same factory as candies with nuts.