This can be a time consuming achievement, but very simple to complete. Here's the list of candy buckets you must visit:

Alliance

1. Dun Morogh, Kharanos
2. Duskwood, Darkshire
3. Eastern Plaguelands, Light's Hope Chapel
4. Elwynn Forest, Goldshire
5. Hillsbrad Foothills, Southshore
6. Hinterlands, Aerie Peak
7. Ironforge, The Commons
8. Loch Modan, Thelsamar
9. Redridge Mountains, Lakeshire
10. Stormwind, The Trade District
11. Stranglethorn Vale, Booty Bay
12. Westfall, Sentinel Hill
13. Wetlands, Menethil Harbor

One way to go about this is to start from the top of the map and work your way down. If you follow this route, visit the following cities in this order:

1. Eastern Plaguelands, Light's Hope Chapel
2. Hinterlands, Aerie Peak
3. Hillsbrad Foothills, Southshore
4. Wetlands, Menethil Harbor
5. Ironforge, The Commons
6. Dun Morogh, Kharanos
7. Loch Modan, Thelsamar
8. Stormwind, The Trade District
9. Elwynn Forest, Goldshire
10. Redridge Mountains, Lakeshire
11. Duskwood, Darkshire
12. Westfall, Sentinel Hill
13. Stranglethorn Vale, Booty Bay

From Booty Bay you can take the boat over to Ratchet if you need to complete the Tricks and Treats of Kalimdor

Horde

1. Arathi Highlands, Hammerfall
2. Badlands, Kargath
3. Eastern Plaguelands, Light's Hope Chapel
4. Eversong Woods, Falconwing Square
5. Eversong Woods, Fairbreeze Village
6. Ghostlands, Tranquillien
7. Hillsbrad Foothills, Tarren Mill
8. Hinterlands, Revantusk Village
9. Silvermoon, The Bazaar
10. Silvermoon, The Royal Exchange
11. Silverpine Forest, The Sepulcher
12. Stranglethorn Vale, Booty Bay
13. Stranglethorn Vale, Grom'gol Base Camp
14. Swamp of Sorrows, Stonard
15. Tirisfal Glades, Brill
16. Undercity, The Trade Quarter

One way to go about this is to start from the top of the map and work your way down. If you follow this route, visit the following cities in this order:

1. Silvermoon, The Bazaar
2. Silvermoon, The Royal Exchange
3. Eversong Woods, Falconwing Square
4. Eversong Woods, Fairbreeze Village
5. Ghostlands, Tranquillien
6. Eastern Plaguelands, Light's Hope Chapel
7. Tirisfal Glades, Brill
8. Undercity, The Trade Quarter
9. Silverpine Forest, The Sepulcher
10. Hillsbrad Foothills, Tarren Mill
11. Hinterlands, Revantusk Village
12. Arathi Highlands, Hammerfall
13. Badlands, Kargath
14. Swamp of Sorrows, Stonard
15. Stranglethorn Vale, Grom'gol Base Camp
16. Stranglethorn Vale, Booty Bay

From Booty Bay you can take the boat over to Ratchet if you need to complete the Tricks and Treats of Kalimdor