I'm sorry I must have tried to answer this 10 times and been interrupted each time!! We struggle with this too. Here are some things we do. RE food we pack everything and the instructions are simply, do not feed her anything other than what we provide. This is true for grandparents, playdates, classes, whatever. People who don't deal with food issues can be very illogical about this, like thinking graham crackers don't have wheat in them or fruit loops are made from fruit or who knows what.

I think it is good to set our kids up for success and give them a chance. If you dont' have any specific objection to the friend, talk to the parent, explain that your child has difficulty doing quiet activities with friend around but very much wants to try a play date, set the playdate for a time when it's not movie night or something he can't handle, keep it short, stay nearby with a cell phone so you can be contact (or stay there and visit if that is more comfortable) or if that won't work as the other family if you can get them together at a park or someplace more doable for your son.