There are many items that may have hidden gluten but you also need to watch out for cross contamination.  This happens when items made or served with gluten are also made or come in contact with gluten-free.  
                                                  

If you have celiac disease you know how important it is to maintain a gluten-free lifestyle. In addition to avoiding gluten in foods at home and when dining out, it is also very important to avoid gluten-containing lip balms, makeup, medications and oral care products (toothpaste and mouthwash for instance). However, you also need to be aware of cross contamination. And, there are several potential sources of cross contamination.

Sources of Gluten-free Cross Contamination

Restaurants: Though more restaurants are offering gluten free foods, it is very important to find out how these foods are prepared. Ask the waiter if they are prepared in a separate area on separate equipment and surfaces. You can also write down specific instructions for the chef (chefs learn about special diets in culinary school).  Make sure your salad didn't come in contact with croutons at some point.  When you get your good, ask the waiter again to be sure you got the right food and it still does not have gluten.  Check the food yourself before eating as the waiter may not be aware of a hidden crouton in your salad or that your fish has been breaded with flour. 

Packaged Foods: Don’t be fooled by the gluten free label. Many packaged foods have been processed in a facility that processes wheat, rye or barley. And, that may be okay if the facility is divided and the food batch tested for gluten. However, food prepared on the same equipment will likely be contaminated unless the company thoroughly washes the equipment in between running batches of food that contain gluten and those that don’t. To be sure, call the company and ask how they prepare all foods listed as gluten-free.  Ask if they are certified gluten-free. 

At Home: If you bake with flour, that flour can linger in the air for a day or more after you bake! Therefore, keeping a gluten free kitchen is very important. Experts recommend using non-porous utensils (so gluten doesn't stay in them after cleaning) and keeping a separate toaster, kitchen sponges and bread machine. If you keep both gluten-containing and gluten free foods in your kitchen, be sure to thoroughly clean your oven, countertops, door handles and other surfaces.

Supplements & Medications – if all of the ingredients are not listed (all dietary supplements require an ingredient list), call the manufacturer and ask what is in the product and how it is produced. If it is not certified gluten free it may be produced on a line along with products that contain wheat ingredients.  Look for supplements that are certified gluten free.

Keep a Food Diary to Track Hidden Triggers

If you are still having side effects and can’t find out where they are coming from, keep a very detailed food diary including what foods you are eating, how and where they are prepared (restaurant, at a friends house, your house etc.) and the time you ate. In addition, write down your symptoms – exactly what symptoms you are having and the time. Keep this record and show it to your healthcare practitioner so you can work together to find out what changes you may need to make.