Quick Answer The best Stanley cup for flying is the 30oz or 40oz Quencher with a flip-straw lid — it fits standard airline cup holders, holds enough water for long-haul flights, and stays empty through TSA screening. For frequent flyers, leak-proof designs with pressure-equalising lids are worth the upgrade. Here's how to choose the right size, avoid mid-flight leaks, and pick a design that actually survives airport life. Why Your Stanley Matters at 30,000 Feet I've been flying with insulated tumblers for years, and the difference between a good and bad in-flight water bottle is something you only appreciate at...