Allergies and other kinds of substance intolerance are a problem for many people, and can be a real hassle while traveling. However, with proper preparation, one can still enjoy traveling safely.
When you are flying from your home, the airplane might not have food that you can eat. Pack some food with you for the first leg of your trip so you can eat safely on the airplane. If your destination country doesn't allow you to import food, you can always throw it away in the airport.
A frequently used option for people with allergies is to stay in an accommodation which gives full access to a kitchen. This allows travellers to go to local supermarkets and buy what they need in order to be healthy.