A.E.
Any kind as long as it's cheap because they take a beating! Also, if you buy it at a Target/K-Mart/Walmart...make sure to buy the extended warranty. We had one that petered out two years after I bought it. I called a number, and voila, they sent a postage paid envelope, I mailed it back, and they refunded the entire amount to buy a new one immediately. Super easy and worth the extra four bucks I paid when I bought it.
PS: Last time I traveld with a young one I brought a huge bag of gummies. My two year old swallowed gum so that wasn't an option for his ears and the de-pressurization. I bought big gummy worms and stuff to keep him chewing so they wouldn't get too plugged - it worked great. I had a huge bag of all different types (spiders, worms, octopus, martians, flowers, butterflies) on our last flight, and donated them to some parents that had a screaming kid. He stopped crying immediately, and the entire flight crew came up and thanked me when I got off the flight.