Help me plan for everything!

[NerdHut]

My players are in a town which was recently attacked by an army of goblins. The army is gone, but as the attack came without any warning whatsoever, the city guard has been ordered to close every gate in the city, and only allow authorized individuals through. The party needs out of the city, but they're not among the authorized individuals. I intend for them to try to sneak out through some means, but I want to be able to plan for several possible methods. The problem is that my players often think of something I haven't and I have to improvise something, and it usually plays poorly.

I'd just like you guys to tell me what you would personally do to try to weasel your way out of a walled city, so that I can plan for that possibility.
The players are all level 3, btw. There is a rogue, cleric, ranger, monk/paladin, and factotum

[Thurbane]

The classic method is out through sewers or similar means, if any exit outside of the city.

Stealthing past the guards.

Charming or incapacitating the guards.

Flying or teleporting (unlikely at levels 3).

Diplomacying their way onto the authorized person list.

Forging documents or otherwise bluffing the guards into thinking they are authorized. Maybe using disguise for the same outcome.

[Braininthejar2]

Rapelling off the city walls - perhaps the guards there are less vigilant.

[Name1]

They could use a catapult and feather fall, I guess. They could also attempt to impersonate/murder the guards or blackmail them by holding their families hostage to ensure the gate they want to use isn't guarded.

[barakaka]

The rogue and the factotum will for sure try to blow a hole in the wall to escape. You can count on this. 100% chance of those two precipitating explosives. A friend of mine has played both of those classes before, and he's the first proponent of using items to solve problems. Watch out for them trying to find gunpowder or using Explosive Packs (Secrets of Sarlona). Explosive pack can be made with a Profession: Siege Engineer check to increase its damage to objects.

If they fail to blow a hole in the wall, then they may try to dig their way out, like some sort of prison break. Or they may try to down potions of Gaseous Form or something to slip through cracks in the wall.

Have your guards make regular checks on homes and establishments trying to find anyone making a daring escape through a hole in the ground/wall. Catapults should be well guarded; you never know when an adventuring party could commandeer one to fire themselves from. It's also possible that a friendly ghost or psion could telekinetic thrust them over the wall. Given enough time, the PCs may just hack and slash their way through the wall. This would probably take forever if none of them has the Mountain Hammer maneuver from an item.

[Thurbane]

Make a hole in an unguarded section of city wall (Stone SHape, adamantine weapon, or just plain old digging).

[Sandsarecool]

Have several loose ideas based on what you think they'll do. You should have a basic feel for their strengths and weaknesses; plan accordingly. Evil/Reckless/Combat-oriented PCs are more likely to just go and take the guards out, especially as a result when PCs:

Buy/commandeer something FAST, and rush A.
Ye olde distraction.
Smuggler's guild. (No black market?)
Goodie-Two-Shoes no accept bribes.
etc.

If you want to try to prepare less, give them several (3-4 work well, usually) options, and as always, give them several attempts to 'notice' these easier methods out. With some luck, they'll wise up and take one.
Then again, depends on your party.

[lytokk]

My first thought was to escape through the sewers/wastewater system. There has to be a way for water to get in and out. This could be blocked by heavy iron bars which would require a very high escape artist check to get through, or maybe just a locked gate where the lock is currently underwater, thus making any check to unlock it much more difficult.

[NerdHut]

Turns out they went with a version I had thought of myself. I hadn't mentioned the rogue was a pixie, because I knew alllllll the suggestions would use polymorph or permanent image. And that's what they did. The pixie impersonated the Duke so they could be granted permission into the city. Probably a good thing the strictly lawful good paladin/monk missed that session......