If you are trying to go the gluten free route, here are a few ingredients you might want to be wary of.
Natural Flavor: This doesn't always mean that there is gluten in a product, but often monosodium glutamate (MSG) is hidden under "Natural Flavors". MSG doesn't always contain gluten, but you need to watch for it to see if it specifies.
Monosodium glutamate: As listed above. If it doesn't specify that the MSG used is gluten free, be wary.
Emulsifiers: These are used as an egg replacer and can contain gluten.
Lectins (lechithin): These are made from the hull of a grain. Some of the grains used are safe, but this is another ingredient to be careful with.