Basic things that my children love and that I remember from being a child (my parents couldn't afford or didn't think were important on top what they had paid for)--Buy the balloons if they want them the first day, buy the water sprayer and bring back each day, but the popcorn bucket in a park, let them stare in windows on Main St. Let them spend time shopping or browsing after a ride and let them pick something small (you mentioned the pins, keychains etc) especially if your daughter likes Frozen (you will need a LL or G+). My daughter bought a small Elsa necklace, one trip and a doll the next, but she felt empowered picking it and wears it to school still. I remember my time in the gift shop obsessing over an Ariel figurine in the late 80s as much as anything else we did. Whatever their favorite character or movie is, let them buy that souvenir (it's a vacation), and meet that character. In the Magic Kingdom the Festival of Fantasy Parade is a magical experience for children and worth the trouble of finding a spot and staying there 30 minutes before.