Here's an interesting shopping app that could help you find foods that are safe in the supermarket. I haven't tried this myself so I can't vouch for it -- I know I'm behind the times, but I'm just not one of those people who carries my phone everywhere I go -- but it may be worth checking out.
It's called Content Checked and apparently, you use it to scan bar codes and it will tell you if the product has allergens that you can't eat. You store your allergens in the app so it knows what to look for.
Anyway, it looks interesting, so here's the website if you want to check it out: