No matter where you go, whether it's a Spanish-speaking country or local hubs in the Spanish-speaking community, you're going to run into people that speak varying degrees of English. While this may be a big help in survival or critical-need situations--like if you're running late to a business meeting or need help finding a safe place to sleep--making the most of your Spanish immersion experience means avoiding translations from others as much as possible.
You should also resist the urge to carry a hefty comprehensive Spanish-English dictionary for reference. Limit yourself to a small travel dictionary or phrase book that you can stick in your back pocket, and pull it out only for emergencies. Learning by immersion is like jumping into the deep end of the pool, so this is written with the assumption that you have at least a very basic command of some vocabulary and a few basic verbs.
After all, if you can't swim at all--to continue the analogy--there's not much point in your jumping into the deep end of the pool, is there? But as long as you have at least the basics of paddling under your belt, you'll get some benefit from the practice. And, the more theoretical knowledge you have, the faster you'll improve--leaps and bounds--as you learn to properly apply it.
As counterintuitive as it may sound, one of the keys to learning a new language by immersion is not obsessing too much about what you understand or don't in the streams of words that pass you by. Obviously, you want to get the gist of what is said as often as possible, but you should enter the experience having already accepted that there will be a lot you won't understand at first. Don't try to make a mental list of every word that goes by and then recall its English correlation.
Instead, just listen for a while without fretting about comprehension at all. Get a feel for the rhythm and flow of conversation around you, and let yourself acknowledge that some words are familiar without fretting about what they mean. Doing this is like the difference between looking at a forest (the conversation as a whole) or individual trees (focusing on each word as it goes by). You'd never get anywhere if you looked at a vast forested landscape one tree--one word--at a time. But, if you take in the entire forest at once, you'll have a chance to gather at least some useful impressions from it.