For travel, "understood" beats "grammatically perfect" — a handful of practical phrases goes a long way.
The essentials
Greetings, please and thank you, and the small courtesies that open doors. A warm "buenos días" and "gracias" set the tone for everything that follows.
Getting around and getting fed
The phrases for directions, transport, ordering, shopping, and paying cover most of what a trip actually demands day to day.
When things go wrong
Knowing how to ask for help, and the words for a problem or an emergency, matters more than any amount of grammar when you actually need it.
Confidence over perfection
A friendly attempt in Spanish is almost always met warmly. You don't need fluency to travel well — you need the willingness to try and a few reliable phrases.