We're so lucky to have a fantastic group of friends who really get it about Andrew's allergies. They're careful to bring over "Andrew-safe" food for potluck dinners at our place, and they're sometimes even more careful than I am about checking out all of the ingredients.
When we went on our Summerland vacation, Sarah even wrote out all of the ingredients for all of the home-baked cookies that she brought, and had us look them over to make sure that they were safe. Because of course, while Andrew doesn't really care about curries and other grown-up food, he does love cookies and anything else that looks like it has sugar in it.
I think the turning point for our friends might have been the time I let Andrew (at around 2 years old) have a taste of some gelato ice cream, and he threw up all over me after two licks. (I gave it to him because I wanted to see if he'd outgrown his dairy allergy.) You can tell people that your kid has an allergy, and they might think that it's not a big deal. But after they see him get violently sick, they take it a lot more seriously. I love our friends for taking care of us so well.
The same thing goes for the grandparents. My mom's been there for two of his peanut reactions, and afterwards, has been so mad at herself both times. She's gotten so much more careful now with what she buys for him -- and when in doubt, she now has the backbone to tell him "no." Which is hard for her, because she always says "yes" to anything he asks for. Once she figured out that he could ride a bike, she even took him to Toys'R'Us and let him choose any bicycle he wanted. Yeesh. Talk about a spoilt grandson!