It feels overwhelming to realize that anything you put in your mouth may be "poison". This will make you want to gravitate towards anything that says "gluten free" on the label just so you feel safe. Don't feel like you need to spend a fortune on replacement foods. GF pastas, breads, etc can be expensive.
Start with the basics. You can eat any fresh meat, fruit, vegetable. You can also eat eggs and rice. Be calm, be methodical, don't panic.
Go through your cabinet and check the seasonings/spices and condiments you routinely use. Most will probably be safe! Use a big sharpie marker and mark everything you have that is safe. You'll want to keep using the sharpie on all of your edibles until you get the hang of it.
Now repeat this process with your pantry items. Many things (canned veggies), will be fine. Most soups will not. Pasta and breads, obviously, are out of the question. Check the page titled "where's it hiding?" for the words that - from now on - mean "inedible".
You will rapidly figure out the items that you are used to using that need to be replaced. After all, most of us repeat the same 20 recipes over and over.