What is your school's snack/birthday treat policy? Many schools now have a policy that if the treat is not suitable for the whole class, including the allergic child, it is not to be brought in. Same goes for homemade baked goods, due to possible cross contamination issues in the baker's kitchen. That is why they suggest store bought pre-packaged items with a label on it.
If your school does not have a policy, and you still are going to bring in the bakery cupcakes, some if the items that I know are OK for peanut allergies are: SOME (not all, must read label) snack cakes (no Little Debbie for sure),
Chips Ahoy cookies (brand label, NOT store brand), Fruit Roll Ups, Fruit By the Foot, etc. and our favorite Krispy Kreme Donuts!
My DD has a peanut allergy and sometimes if she is at a Girl Scout event or party outside of school, the moms make her up a little bag of safe candy instead (Starbursts, Nerds, Smarties, DumDums)
I don't do baked goods anymore for her class birthday treats, DD passes out Nerds Ropes tied with a ribbon and a little tag that says Happy Birthday!
I used to wrap a pencil with it too, but got too costly that way.
Hope that gives you some direction and idea...