Japan trip — how did you handle soy sauce?

Seconding the tamari. Also grab a translation card from the Chef Card tool here before you go — showing written Japanese to the kitchen gets taken far more seriously than pointing at a menu.

Learn 'gluten free' in Japanese (グルテンフリー) and show it at the door — it works surprisingly well. Rice-based dishes like sushi and grilled fish are your safest bets, always confirm the broth in noodle soups. Carrying mini tamari bottles saved me more than once.