If you're with Abdul and talk to one of the merchants on the southeast side of town, he'll be revealed to be an aquaintance of Abdul's, and they'll catch up on old times. Abdul's FP will go up by 1 afterwards.
Requirements: Abdul is in party, above event has been triggered
After you've met Khalid, a young woman will appear on the west side of the map on days 30~36. Talk to her for an event, and Abdul's FP will go up by 2.
Requirements: Iggy is in the party
If you buy shwarma from the merchant on the southeast part of town and Iggy is with you, you'll get an event. You can scold him for +2FP, ignore him for +1FP, or give him more for no FP but -some bad karma. If your stand is Wildhearts, you get some extra dialogue after your decision.
Requirements: Jotaro is in the party
There's a merchant outside where you can buy Diamond C for 500G. If you buy it, however, he'll scam you by switching the bills in his sleeve, and it will actually cost 740G. If Jotaro is with you, he'll notice this, and demand the merchant pay back the money. However, the merchant won't fess up, so Jotaro will leave - on his way out, he'll secretly take back the 60G and 10x Diamond C, which will be added to your inventory. His FP will also go up.
Ultimate Junk Food
Requirements: Joseph is in the party
Talk to the merchant selling Sweets and Sponge Cake with Joseph in the party, and he'll tell you about American snack food and gain +1FP.
Requirements: Polnareff is in the party
Talk to the merchant in the hotel with Polnareff, and Joseph will crack a joke. Polnareff's FP will go up by 1.
In the southwest corner of the map, there's a woman in a chador. Approach her, and your ears will start ringing, decreasing your SP - talk to her to fight Amber. If your Stand is Deep Purple, you'll learn the Mirage skill after you defeat her.
Requirements: Have cleared the game 3 times or more, beat Utah in Hong Kong but not at the Harbor, current day is under 22, Sword Of St. George not in inventory
In the upper-right corner on the map is a familiar face who only appears if you're on your 4th playthrough and up and have fulfilled the above requirements. Defeat him for a Badge of Honor and the Rusty Sword.
To the left of the Inn's door, you can find a secret spot between the first and second set of windows where attempting to walk up into the wall results in a 'knocking' sound. Continuing to do this will see each knock have a chance to allow you into a secret area (the chance is random with each 'knock', so it may take a random period of time to get inside.). Once inside, you will be in a 'ghost house' with one human occupant. Despite what he says, you can't rest here. However, beyond the top left door is a area containing the spirits of all the characters who have been killed or retired in some way, shape, or form (By your or your party's hand or not, including both key characters, innocent bystanders killed along the way, and optional bosses) up until this point in the game. Barring the 'man in a suit', a jester-like resident, and a corpse, all of the characters here can be walked through. To talk to them, you must stand inside of them and interact, rather then the traditional style of them being in front of you.
Aside from listen to the moans and curses of the dead, there is not much one can do here at this point. The Man in a Suit blocks your way to a critical door and is not a ghost, so cannot be walked through. The upper right door in the ghost area cannot be entered due to leading to the afterlife and you are still alive. (The jester even advises you that you cannot use that door), the top-right door in the main room is a inaccessible bathroom, and as of right now, it is not known if you can find any items of use, and most items in the main room either have little interest to be interacted with, or the human occupant will stop you from using it. There is a bit of advise given by the corpse however, and interacting with the sink in the main room of this secret area will grant you free bottled water. Take note however... that there is no way to save or use items in here. Due to the fact that the menu is disabled entirely while in this area. Likewise however, there are no enemies or encounters to be found here.