Generally you don't enter a bar/restaurant except to use the loo, get directions, have a drink, or eat a meal; hence there is no absolute need for a large vocabulary to buy food. Smiles and the basic words hola, por favor, cuanto and gracias will take you far. Also learn to point!!
Many years ago walking west from Leon on the CF in pouring rain at Villadangos del Páramo I staggered dripping and exhausted into a truck stop. What a way to make an impact! The place was packed with about 80 VERY macho men whose lorries were parked in front. All seemed to be eating the menu del dia or special daily menu. When the flustered young waiter rattled off the main course choices l pointed towards the nearest customer's plate, nodded and said por favor. The food was copious, hot and delicious.
At dessert time half the room seemed curious about what I would choose. I pointed to rice pudding, but fruit and chocolate cake also appeared on my table por la fuerza en el camino. As the truck drivers left for their coffee served at the bar most waved and wished Buen Camino....All these years later when necessary I still point.