DIY busy board full of switches, latches, and doo-dads for babies and toddlers to manipulate. This is great for fine motor skills. It is also a hazard for giving escapee toddlers the skills they need to get out unsupervised.
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.