You can use a variety of meats, veggies and fruits. We even managed to find 2 gluten free marinades (pictured above, gluten free at the time of this post) at the store. There are plenty of homemade marinades to choose from that are gluten, dairy, egg free as well if you start searching. Allrecipes.com or Yummly.com are great places to browse in addition to Pinterest or Google searches.
Here are some ideas:
pork, chicken, shrimp, beef
onion wedges, bell peppers, summer squash, tomato
fresh pineapple, peach chunks
If you're using wooden skewers, soak them prior to use so they don't burn while grilling or broiling. It's a simple thing to make. Cut your meat into chunks and marinade; you can marinate the veggies too. Skewer meat and veggies/fruits alternating and cook till meat is done. I found that my kids enjoy the meat the most, so I make them ones with extra meat and ours with more veggies.