Eggs are fine - it's what they eat while they're developing and hatching anyway .
If they're 13 weeks and have had any sort of time on the ground, or if you've given them any grit, they can eat pretty much anything a grown chicken can eat. Plus the more variety you offer them the more likely they are to accept new foods later. Meat is ok (extra protein) - fish, chicken . . . just don't go nuts. They should still get a majority of their food from the grower feed since it has more balanced nutrients - but offer them fruits, greens, bread, yogurt . . . whatever leftovers you have. Stay away from avocado (although it's not 100% determined to be toxic there is some speculation). Just bring it on and see what they like - you'll be amazed at the little chow-hounds.