Food related posts are my favorite ones.
My favorite snack in the parks is a Jalapeno Cheese Filled Pretzel. It's soooooo good. Of course, free tortillas from DCA are also delicious. For something sweet, I love the chocolate covered caramel corn in the candy shops.
I really am in love with Turkey legs, corn dogs, bacon wrapped asparagus (from Bengal BBQ), and fried mozzarella sticks from the Golden Horseshoe. I'm a big eater, so these aren't really "snacks" but just deliciously typical greasy theme park meals. If you share though, I'd say they qualify as snacks
That said, sometimes I feel like there are snacks at WDW or Tokyo Disney Resort that would be great at DLR. Like Kaki Gori or the make your own treats at Goofy's Candy Shop in Downtown Disney. Don't even get me started on the amazing flavored popcorns or the giant gyoza sandwich at TDR