It seems that in some states public possession of alcohol by minors is also illegal. The question then becomes what the definition of “public” is. Again, packing unopened alcohol in a suitcase does not seem like public possession.
The laws are concerned with drunk driving. Most states allow minors to consume alcohol in private (their own homes) or when accompanied by a guardian. So the laws seem to be aimed at stopping public drunkenness, but don’t seem to care about curbing private behavior.
I think a suitcase is private, but, of course, courts might see it otherwise. Personally, I’d take the risk. But then, I’ve smuggled illegal food items into the country. For that matter, I’ve accidentally packed knives in my fanny pack while boarding a plane, and got away with it.