You can always buy or order Star Wars or Hulk themed merchandise ahead of time and sneak it with you in your luggage. Then you can control what, when, where, and how you want to give it to him. Most kids don't care about waiting in line at a store to purchase it. They just remember what and when they got it. I do this sometimes when I want to make something extra special for my kids to make a particular memory for them. I find that sometimes it can be time consuming and expensive to find just the right "gift" at just the right time. Sometimes that works, sometimes not. But when I plan ahead, it has always worked out great.
My oldest is becoming a bit of a SW fan herself. Have already picked out a special SW toy (new) they have since stopped selling in the parks on Ebay. I plan on giving it to her next time we visit WDW.