Start with the seat
Try the outfit in a chair for a few minutes before travel day. A waistband, thick seam or tucked-in shirt can feel quite different after you sit down. Trousers with a little room, a soft skirt or a relaxed dress may work well, but the fit of the individual garment matters more than its label.
Check what happens when you reach upwards or lean forward. You may need to lift a bag, use a table or get past another passenger. If a top rides up more than you like, try a different length rather than relying on the outer layer to hold everything in place. Keep pockets free of bulky objects while seated.
Use layers you can change easily
A light top beneath a cardigan or overshirt gives you options if the carriage feels warmer or cooler than the platform. Avoid burying the removable layer beneath a tightly packed bag. A coat can travel on top of the luggage where you can reach it, provided it is secure and not obstructing anyone.
Bring a small bag for the things you want at your seat, such as your phone, book and charging lead. This reduces the need to reach into the main case each time. Keep its strap and handles clear of the aisle and your feet.
The journey includes waiting and walking outdoors, not only the time on the train. Check the weather for both ends and choose shoes suitable for carrying your luggage across the route. If you expect to go straight to a meeting or meal, select a base outfit that works there too. A change of top may be easier than carrying an entirely separate travel wardrobe.
