Hiya Gavin!
Welcome to planDisney! The anticipation is always one of the best parts of a Disneyland Resort visit, and I definitely know the feeling of planning for a souvenir (or two...or three...) in advance!
Getting precious cargo home safely from the parks can be a heroic effort! As far as carrying your new shield onto your flight, I'm afraid those regulations are beyond my command. I would recommend contacting your airline to ask if they have a policy for oversized carry-on luggage. I can tell you that items purchased inside the parks can be shipped directly home, which might be a better option for you! Just keep your receipt and ask the Cast Member who helps you with your purchase about your shipping options and pricing. I've also had wonderful Cast Members go the extra mile to wrap my items safely. I'm sure you'll find the help you need!
If you decide that you do want to carry your shield home yourself then you might want to take advantage of the
complimentary package check service offered at the parks. That way you can enjoy the park knowing that your mighty accessory is in good hands!
While you visit Disney California Adventure Park you should probably grab a snack! Check out the
Disney California Adventure Food & Wine Festival for unique and epic options. Then you can go
Soarin' Over California and pretend you are a high-flying superhero!
Thanks again for your question, Gavin! Have an amazing time at the parks!
Keep moving forward!
Amanda