Sudden jellyfish sting on the south beach — what first aid do travelers actually use here?

Get out of the water, rinse with seawater not fresh water if you can, and carefully remove any tentacle bits with a card or tweezers — not bare fingers. Many locals use a hot compress or a pharmacy sting gel after; vinegar is used in some places but do not invent a home remedy from a meme. If breathing feels odd, the sting covers a large area, or pain keeps climbing, go to a clinic. Mild raised welts often settle with basic care and rest. I will not quote a fixed clinic price.