Special equipment: a large punch bowl
Mix the cranberry juice, orange juice and pineapple juice in a bowl or large pitcher. Gently stir to combine. Fill 2 ice cube trays with punch and freeze until solid, about 3 hours. Place remaining punch in the refrigerator to chill.
Transfer the punch to a punch bowl and stir in the ice cubes, vodka, strawberries and pineapple. Divide the punch among 6 glasses, add a splash of seltzer to each glass and serve.