We carry epipen and epipen jr for two of our dds (severe allergy to insects, bees, hornets, wasps, etc.).
They react so quickly that we have to have the pens practically in hand, its so stressful. We found great little plastic holders (belt clip type) at either Walgreens or CVS, can't remember and they are designed specifically to hold the epipens. Think they were like 4 bucks or so and just made life easier for us, maybe its psychological but we feel better with it so close at hand.
We also carry the benadryl meltaways.
One dd got stung in Epcot in 1993 and the experience while extremely stressful was handled so well by Disney in terms of getting us stable and out of the park. They even followed up with us later.
We have never had an issue flying with the epipens, but always carry the original label just in case. We also always carry two per child as someone else said.