The full answer
Backup snacks and a few key essentials
Packing gluten-free snacks (bars, crackers, or similar shelf-stable options) as backup for delays or limited food options is one of the most useful things to bring — it removes the pressure of needing a safe meal immediately available at all times.
Other useful items
A translation card explaining celiac disease in the local language (see explaining celiac disease abroad) and a list of safe restaurants or grocery stores researched ahead of time can make a real difference, especially on multi-day trips.
Important context
Individual symptoms, reactions, medical histories, food products, and local labeling rules can vary. Community experiences are not medical evidence.
For personal medical decisions, diagnosis, testing, or treatment, consult a qualified healthcare professional.