Unemployment for under 25s in Spain stands at over 50% right now. I'm guessing it could be even higher in Cadiz, as it's always had one of the highest unemployment rates. Young Spaniards are pouring out of the country in search or work in the UK, Germany and Latin America. So - it may not be the best time to look!
Also - what's your nationality? If you're from outside the EU, you're unlikely to find work legally.
Sorry for the negativity, but it's probably best to be prepared before you jump on a flight!
Without Spanish, you could possibly look for work at an English school summer camp - they may be looking for activity leaders etc. These kind of organisations would be recruiting people from abroad, whereas you are unlikely to secure bar work in Cadiz from your home country.
Suerte!