Melt butter in a skillet over medium-high heat. Add celery and onion; sauté 5 to 6 minutes or until tender.
Combine cornbread, croutons, and crackers in a large bowl; stir in onion mixture, broth, next 3 ingredients, and 1/4 teaspoon salt.
Microwave squash halves on HIGH 5 to 7 minutes or until tender.
Sprinkle squash halves with remaining 1 teaspoon salt; place in a 13- x 9-inch baking dish. Spoon 1/4 cup stuffing in each squash half.
Bake at 375° for 30 minutes or until stuffing is lightly browned.