msg triggered my migraines...
...but I'm lucky; my sensitivity increases and decreases cyclically. This has allowed me to discover that I can tell when it's in a food--sometimes I'll take a bit and just know that it's there.
Have you tried making your own bars? You can add oats, flour, dry milk, fruit juice, nuts, tvp, dash of salt, cinnamon, etc--just make them wet enough to press into the bottom of a pan, bake them on warm til they're dry, and cut them before they cool. They keep in the freezer.
If you're sensitive, you can read the label on any packaged food, then make it at home without the unpronounceables. Saves $$$, and calories, and exposure to substances with negative value.