cardboard tubes + box = hours of fun! We pieced together TP and paper towel tubes. Used marbles. The kiddo loved it and even still pulls it out to roll the marbles into a dump truck. He wont' let me toss any cardboard tubes now.
Juice Box Walkie Talkies are low-budget recycled crafts which help to create many games for children. Your little munchkins will have the best time playing spy or whatever other creative activities for kids they come up with.