They have a gutload you can buy from the petstore but typically I feed crickets romaine lettuce or other healthy fruits and veggies. You can dust them with calcium and vitamins to make them more nutritious.
If you try to feed them something different each time they will get a nice variety of nutrition. I feed apple, potato, carrott, peas, greenbeans, banana, turnip greens, kale, collard greens, spinach, orange, pineapple, zuccini ~ basically whatever I have on hand. I rotate the veggies I feed my bearded dragons so usually I just toss a chunck of whatever they are getting into the cricket bucket. If the crickets are in a closed container watch that you don't add too much in the way of wet food ~ they need some moisture from these foods but if it gets too wet it will kill the crickets. And that really stinks :dizzy2: ! Try putting in one piece of whatever food you have on hand and peek in every once in a while to see how long it takes them to eat it. You'll get the hang of how much to feed then :main_thumbsup: