Should a child who reacted to blueberry with full-body hives and swollen lips carry an EpiPen (epinephrine)? Blueberries seem easy enough to avoid.

Don't assume. Not the blueberries; willing to bet. 25 yrs an allergist, true cases are exceedingly rare. May not be even food. May not even be anaphylaxis; just idiopathic urticaria with angioedema. See an allergist. Why label and carry epi unneccessarily? Sounds like you have enough on your hands. Just saying. Get allergy consult and accurate testing. .
Yes. It is probably in your child's best interest to have an epipen (epinephrine) available. You never know what could be the next food to precipitate an allergic reaction. You would not want to be without that protection should an allergic reaction be severe and life-threatening. Yes it is easy to avoid blueberries, but similar foods could cause the same reaction.
Be prepared. Ask your doctor if you or your child should be prescribed EpiPen, (epinephrine) so that when you recognize the symptoms of anaphylaxis, you can be prepared and use it.