Most cities have extremely minimal supplies of even what you'd consider the basics of life today, due to the way that supply chains have developed. Food is grown far outside a city's borders and transported in, and similarly for medicine; water purification and sewage processing is situated near large fresh water sources, and the treated product is piped in.
The stocks of the above are going to run out fast. Once everyone realises that, they're going to head for the shops to try and stock up on whatever they can. Those shops aren't going to sell those supplies because the owners know that they'll need them before long (also because currency is now worthless). The end result will be rioting, looting, and general anarchy - and that's before supplies run out.
The end result of the fighting will be the development of factions that control various vital resources. Depots of bottled water, police stations with guns and ammunition, that sort of thing. Everyone else gets to survive with whatever they had, or can steal, or whatever.
They don't survive long. A human can survive for weeks without food, but only about 3 days without water. If there is a water source on this other world, one of the powerful factions will already have claimed it - but that's not worth much, because they also need to purify it, and that's a far more difficult task. An organized faction may be able to accomplish this... your average family unit, not so much. And that faction is not going to be willing to allow outsiders to use "their" water.
So people are going to start dying. Lots of people. Because you no longer have clean water or sewage processing or refuse removal or law enforcement or medical services or anyone that has time for tasks other than personal survival, the dead are going to lie where they fall, and they are going to rot. Which will bring disease. Which will make it even more hazardous for those who remain.
Pets of deceased owners will become feral. Rodents and cockroaches will emerge from the sewers. These animals will also be desperate for water and food, which will remove their fear of humans, creating another hazard. They will feast on the dead, which will further generate and spread pestilence.
Unless you are already prepared for such a nightmare scenario, there is very little you, as an average Joe, are going to be able to do to survive it. It doesn't matter how fit you are - if you can't get the essentials of human life, you die. Even if you have superpowers, unless those powers are "produce clean water", you're done for.
So, the #1 predictor of survival in this scenario, is, perversely, how quickly you get out of the city. The sooner you leave, the sooner you will (hopefully) find a (relatively) clean water source that (probably) won't kill you. If you're lucky, you find native plants that you can eat (you will certainly lose a few of your people to the trial and error necessary in figuring out what's poisonous and what's not). If you're really lucky you have some Earth crop seeds to plant, and you find somewhere to plant them, and you actually know how to make them grow, and they don't get eaten or destroyed by rain or native animals, and they produce enough to feed everyone in your group...
All of this is ignoring the deadliness of the native fauna on this world. That includes bacteria and viruses (or whatever the native equivalent is), which as H. G. Wells demonstrated, could conceivably be the deadliest thing of all.
Finally, the world in question needs to be broadly similar to Earth for humans to have any chance of surviving. If you're talking non-carbon-based lifeforms, or and extremely arid planet, or a different atmospheric gas composition, you might as well be on the Moon or on Mars.
In short, what you have is a situation that's at best orders of magnitude worse than any zombie apocalypse. 20% of the population surviving would be a miracle; I think 2% would still be a stretch.