For the past few days there has already been a significant build up to San Juan (also the Summer Solstice) here in VnG. Firecrackers being the most noticeable thing, being set off at all hours of the day all over the town, and also the bonfires which are springing up in the various barrios.
Both bonfires and fireworks play a huge part in this festival with many of the barrios staging their own parties and an all-nighter that goes on on the beach.
Of course drink is involved to a degree, but although thee may be plenty of noise and rowdiness there is unlikely to be any trouble.
To allow everyone to recover from the night of revelry the 24th is a public holiday, so don't expect to get any shopping done that day.