In a small saucepan cook potato, covered, in boiling water for 20 to 25 minutes or just until tender. Drain well; cool slightly. Peel and cube potato.
Meanwhile, for dressing, in a medium bowl stir together mayonnaise dressing and mustard. Add potato, carrots, sweet pepper, onion, and relish to dressing. Toss lightly to coat. Cover and chill for 2 to 48 hours.
Spoon into 4 containers; cover tightly. Pack in insulated containers with ice packs. If desired, serve with pickle slices. Makes 4 (1/2-cup) servings.