Yes, you are absolutely allowed to bring your own food, including sandwiches, onto the Eurostar. Unlike air travel, there are no restrictions on solid food passing through security at London St Pancras, Paris Nord, or Brussels Midi. You can also bring non-alcoholic beverages, though there are specific limits on alcohol (typically one bottle of wine or four beers per person). However, a critical 2026 update involves post-Brexit customs regulations: while you can eat your ham or cheese sandwich on the train, you generally cannot bring meat or dairy products into the EU from the UK (and vice versa) due to strict phytosanitary rules. To avoid issues with customs officers upon arrival, it is best to consume any fresh sandwiches before you disembark or stick to vegan/vegetarian options that are less likely to be seized.