Yes, you are welcome to bring your own food on board Finnair flights, provided it complies with airport security regulations regarding liquids. Solid foods like sandwiches, fruit, or snacks are perfectly fine to bring through the checkpoint and consume during the flight. This is a popular option for travelers in Economy Class on short-haul European flights where meals are typically only available for purchase from the "Nordic Kitchen" menu. However, if you bring your own meal, the cabin crew is unable to heat it or refrigerate it for you due to safety and hygiene protocols. For long-haul flights to Asia or North America, Finnair still provides complimentary hot meals in all cabins, but bringing your own snacks is still allowed. If you have a severe nut allergy, it is recommended to inform the crew upon boarding; while they cannot "guarantee" a nut-free cabin, they can often make an announcement to nearby passengers asking them to refrain from opening nut-based products.