|Tiny Coffee Golem|
You're one of two groups. You're either attacking or defending a city.
Attacking: you're a small adventuring group. 4-6 powerful individuals. The details are at your discretion, but lean toward the "realistic." You're resources are vast as is fitting your group, but not endless. The end goal would be to get some specific treasure or conquer the city for yourself. Killing the ruling body (see "defending") would be required for that. You know as much about the city as the common people know and perhaps just a touch more as would come from a high gather info check + a few divinations.
Defending: you're a standard 4-6 adventuring group who years ago conquered and setted a now thriving city. You have a reasonable standing army and base of operations. Your resources are vast, but you still have a kingdom worth of upkeep. Be creative, but consider the cost/benefit ratios.
For both groups the details are up to you, but please consider what a "reasonable" dm would allow. Custom items, sure. Snow cone wish machines, probably not.
Feel free to reply to other posters with countermeasures. "Cities probably have lots of archers to counter flyers," for example.