"¿Cuánto cuesta sin propina?" (How much without tip?) - useful at restaurants with automatic service charges.

"¿Hay descuento por efectivo?" (Cash discount?) - many places give 10% off for cash vs credit.

"Soy alérgico a..." (I'm allergic to...) - crucial for food allergies since menus don't always list ingredients clearly.

"¿Dónde está la parada de autobús?" (Where's the bus stop?) - more useful than asking for expensive taxis.

Learning these took my interactions from tourist-level to getting local prices and recommendations.