Combine water, milk, salt, sugar, and corn starch in a saucepan over medium heat. Add butter and bring to a boil. Remove from heat and stir in flour. Place back on stovetop, stir until liquid evaporates, then mix in eggs. Transfer dough to a piping bag with a star nozzle.
Place 7 glass bowls (4-inch diameter) upside-down on a baking tray lined with parchment paper for larger cups. For smaller cups, use 7 glass bowls (3-inch diameter) on a second tray. For a large singular cup, use a 5-inch glass bowl on a third tray. Grease and flour the outsides of the bowls and pipe dough over them. Bake at 350°F for 1 hour until golden brown. Remove and let cool for 1 hour.
Fill the large churro cups with an assortment of snacks like raspberries, marshmallows, pretzel sticks, grapes, blueberries, banana slices, and mixed nuts.
Cut a plastic straw into 7 equal pieces and push them through evenly-spaced points in the large singular churro cup.
Place a tall drinking glass upside-down in the middle of the larger churro cups ring. Slide the smaller churro cups ring over it so that it sits on top of the larger ring. Place the large singular churro cup on top of the glass.
For the white chocolate ganache, heat white chocolate chips and heavy cream in a saucepan over low heat until melted. Stir to combine. Repeat for dark chocolate ganache with semi-sweet chocolate chips and heavy cream.
Pour both ganaches into the large singular churro cup at the same time so they mix and run through the straws into the small churro cups ring beneath.