-Soda or Club Crackers
Peanut Butter Cheerios
Various snacks (cheese, pretzel sticks. carrots, goldfish crackers. marshmallows, etc.
Use the cracker to make the train cars, the cheerios for the wheels, and the other items for the cargo for the train. For example: They could have one cracker and have a flat car and stack it full of pretzel sticks for logs. Anything works we even had flying trains.