Here is a list of all cities in the game, with every items you can find in their shop, and every destinations for their airport. As far as I know, it's totally fixed and never randomized, so it's useful to know what you'll find in a city before entering it, to plan your future strategy. But if we find that there is some sort of RNG for those elements, I'll modify the guide accordingly.
BEIJING Shop: Owl’s feather / Delicious meat / Sleeping potion / Purple bell Airport: Cairo / Rio De Janeiro / London
BERLIN Shop: Whistle to call a bird / Traveler’s ring / Heart gloves / Green bell Airport: Rio De Janeiro / San Francisco / Hong Kong
BUENOS AIRES Shop: Royal family’s ring / Harp to call thunder / Green bell / Airplane ticket Airport: Moscow / New York / Kyoto
CAIRO Shop: Phoenix’s feather / Whistle to call a snake / Mysterious treasure box / Airplane ticket Airport: Beijing / Calcutta / Sydney
CALCUTTA Shop: Migrant bird / Whistle to call a snake / Mysterious treasure box / Airplane ticket Airport: Rome / Cairo / Rio De Janeiro
HONG KONG Shop: Traveler’s pendant / Giant’s lamp / Mysterious treasure box / Airplane ticket Airport: Cairo / Rio De Janeiro / London
KYOTO Shop: Royal family’s pendant / Whistle to call a bee / Acme A1 Meat / Airplane ticket Airport: San Francisco / London / Bueno Aires
LONDON Shop: Whistle to call a whale / Spade boot / Diamond boot / Blue bell Airport: Sydney / Hong Kong / Beijing
MOSCOW Shop: Whistle to call a whale / Banana peel / Magical magnifying glass / Red Bell Airport: Buenos Aires / Kyoto / San Francisco
NAIROBI Shop: Merchant’s pendant / Mysterious treasure box / Mysterious treasure box / Airplane ticket Airport: Paris / San Francisco / Hong Kong
NEW YORK Shop: Phoenix’s feather / Soldier’s ring / Discount Card / Yellow bell Airport: Hong Kong / Buenos Aires / Paris
PARIS Shop: Soldier’s pendant / Harp to call rain / Red bell / Airplane ticket Airport: Nairobi / Beijing / New York
RIO DE JANEIRO Shop: Soldier’s pendant / Harp to call rain / Red bell / Airplane ticket Airport: Berlin / Beijing / Calcutta
ROME Shop: Migrant bird / Monk’s ring / Yellow bell / Airplane ticket Airport: Calcutta / Sydney / New York
SAN FRANCISCO Shop: Flying carpet / Meal-in-a-can / Purple bell / Airplane ticket Airport: Kyoto / Nairobi / Moscow
SYDNEY Shop: Monk’s pendant / Harp to call storm / Blue bell / Airplane ticket Airport: London / Rome / Cairo
As an additionnal information, here is the prize for every item in the game. It could also be useful to plan your purchases in advance. I must mention I found those datas here: https://gamefaqs.gamespot.com/gba/471242-tweety-and-the-magic-gems/faqs/14143 You can find other infos with this link if you want.
Acme A1 Meat: 20 CP
Airplane Ticket: 100 CP
Banana Peel: 10 CP
Blue, Green, Purple, Red, or Yellow Bell: 30 CP
Club Hat: 30 CP
Delicious Meat: 10 CP
Diamond Boot or Spade Boot: 30 CP
Discount Card: 30CP
Flying Carpet: 50 CP
Giant's Lamp: 10 CP
Harp to Call a Storm: 30 CP
Harp to Call Rain: 20 CP (It's not written in the FAQ, so I had to verify in the game)
Harp to Call Thunder: 30 CP
Heart Glove: 30 CP
Magical Magnifying Glass: 10 CP
Meal-In-A-Can: 10 CP
Merchant's Pendant: 20 CP
Merchant's Ring: 50 CP
Migrant Bird: 80 CP
Monk's Pendant: 20 CP
Monk's Ring: 20 CP
Mysterious Treasure Box: Varies (In my memories, it can be either 20 or 30 CP)
Owl's Feather: 40 CP
Phoenix's Feather: 100 CP
Royal Family's Ring: 50 CP
Sleeping Potion: 30 CP
Soldier's Pendant: 20 CP
Soldier's Ring: 20 CP
Traveler's Pendant: 20 CP (This one is absent from the FAQ for some reasons)
Traveler's Ring: 30 CP
Turtle Handler's Whistle: 10 CP (Same thing as the Harp to Call Rain)
Whistle to Call a Bee: 10 CP
Whistle to Call a Bird: 20 CP
Whistle to Call a Snake: 10 CP
Whistle to Call a Whale: 20 CP
