Avoid flavoured potato chips and corn snacks then and most prepacked convenience meals they are full of MSG.
There are fewer foods with MSG than there used to be, but you're right, a lot of packaged foods have it. I avoid packaged foods almost completely. I got out of the habit of using them when my allergy first developed, so it isn't a problem now.
I just sometimes get surprised when a home cook uses it. The veg. soup was a surprise, as was a wonderful cucumber salad that I ate a ton of before I got the hint that it had MSG. :-(