Question: Had a allergy question about my son , any allergy docs here

He is seven years old, thank God he has never had a reaction to anything yet. My wife was always scared to give him peanut butter because one of her friends kids had a bad reaction. My mother gave him a Reesie's cup when he was about four and he had no reaction, and my friend XXXXXXX last year gave him peanut butter M&Ms he only had about two of them and then spit it out when he heard my wife say she don't want him to have peanut butter. We only found out about the peanut butter and shellfish allergy when we got him a dog this past Christmas, and when the dog would lick him he would break out in hives. so we went to have him checked and they did the skin test and said he came up positive for peanut butter and shellfish, now just last week we did the blood work that was six months after the skin test. his ige level was 6.09 for peanuts and 5.00 for shellfish.
Now obviously I'm more concerned about what he's eating, but after googling all week I came across where you have to watch out for cross contamination, now I'm concerned because he gets french fries once or twice a week and all the places he gets it from told me that they mix it in the same oil that they do with the shrimp, now in the last four years I've been given him the fries from these places he's never had a reaction, but I'm still concerned what should I do? And then same with milkshakes he gets one or two a week , now I'm concerned because what if someone ordered a Reesie's milkshake prior, I feel bad to take away these things that he's been eating without any problems but now that I know I'm more concerned
Thanks

OK so just to clarify, you think it's OK to keep giving the fries and a milkshake, because he hasn't had any reactions in the last four years I have been doing that, even though they can have some traces of the allergen