And when you decide to become a farmer? Where will you get livestock from? If someone hasn't been feeding them in the last few years, they won't be around. Where will you get seed from? Seeds can survive many years, but only if you store them properly. What power sources will you be using? Horses? Again; unless someone's been keeping those breeding populations of horses alive while everyone is off being Mad Max, at the point the world needs them there won't be any.

Modern farm buildings are modern buildings - they need maintenance. The farms are likely to have fallen down by the time you decide you need to be growing stuff. The fields will be overgrown and overrun. Even if you have fuel for it (alcohol say), a tractor that's been parked for a couple of years may be unusable.

This is actually what will kill everyone else -- by the time they get organised to remember to go and feed the animals at the nearby farms (remember, they're probably locked in and will have a few days food at best), then the breeding populations will be gone. And then you've got five years before the cans and MREs run out.

Note to self: free any animals I pass by that I don't eat. I hope I'd do that anyway out of empathy, instead of leaving them to starve. At least there'd be critters to hunt/recapture then.

5% of the population is still large enough to continue a relative modest civilization. A city of say 1 million people spread out in 100 square miles, means 500 people per square miles still are alive. A city contains an enormous amount of material resources which any surviving peoples would use. These includes guns, fuel, food, shelter, books, electronics, computers, lights, etc.. Though there are zombies about, if they are like zombies in games, they would only be a threat for the first 2 weeks before the remaining humans wipe them out.. A zombie isn't even as smart as a dog, a single human with a shotgun and enough bullets can clear an entire square mile of them, a group of humans can clear out an entire city with enough ammo..

Water might be tainted but luckily water falls from the sky in most places so it would only be awhile before the rains renew the aquifers or reservoirs, in the mean time the survivors can live off bottled water available in the city. Humans would rebuild very quickly as long as there is no systemic threat, which zombies are not unless there is a ramptant infectious disease still on-going making more zombies..

Truthfully even with these circumstances, it's not dire enough to result in a Mad Max type complete collapse world. For that to happen 99.99% of the population has to die off and there has to be massive destruction, destroying not just the people but the knowledge of the previous civilization.. and even then all that would do is set humans back 1-2 thousand years, still not enough to destroy civilization as we know it. Look at the black plague of Europe, 30% of the population died and it only took them 100 years to completely recover that population but civilization didn't stop..

-ddn

The problem I see is *key* people or knowledge. If the people who can keep the phone system, the power system and the transportation system going long-term die, we could eventually become cut off from each other and unable to share knowledge well. This may seem unlikely, but sometimes a single person leaving a company can cause upheaval. It's surprising how much key knowledge is not shared within an organisation, such as admin passwords, where essential files live, the knowledge of which switch to flip when things break down. Sometimes hands-on knowledge is much more important than theoretical knowledge. Also if we lose the ability to create microchips, it would be a long road to get back to that stage.

Like ddn3 said, 5% is a hojillion people, and with a 6-to-1 ratio of monsters to normal dudes, you're looking at one of two possibilities for that battle:

1: Monsters win in a hurry. If they're smart and fast and able to use tools and immune to bullets, they'll storm through the cities killing everyone like a wildfire. The safe havens would either me in a state of permanent siege, fortified against the abominations and struggling to maintain their barricades while sending out heavily armed convoys to load up trucks with supplies, or else the safe havens would be somehow mobile, like a ship or a caravan of fast-moving vehicles. Either way, in a few months either supplies dry up, the havens get overrun or the population is reduced to such a small number of such uncannily qualified survivors that it looks more like The Road than anything else, changing the dynamic of the setting considerably.

2: People win in a hurry. Even if only one in ten survivors are willing and able to shoulder a rifle and fight an army of mantis-men, it's a simple thing for each soldier to get an average of 60 kills against zombie mutant bikers. Some basic strategy, good equipment and common sense will allow the humans to orchestrate situations in which they'll mow down the baddies with ease. Then the situation will be reversed, and you'll be looking at a Fallout scenario: A diminished population rebuilding a smashed society while managing the dangerous wildlife that exists in the wilderness around their settlements. The chief problems here will be people versus people, as they squabble over water rights, deal with unethical leadership or do battle with roving bandits, with the monsters serving primarily as a backdrop.

A good workaround might be to go with the Minecraft paradigm, where beasties are largely inert during the day, but make nighttime virtually useless, leading to a good "build by day/hide or fight by night" system. Link it to the sun, the moon, some kind of semi-predicatble rhythm.

hat way, you can have the enterprising scavengers going out to score phat lewts for sale in the underground bazaar, you can have the bored, incompetent defense force that complacently checks the CCTV cameras every time the airlock activates and waves people in or out, and you can have the elite zed-bashers who go out and actively try to cull the army of darkness. You can have human drama between splinter groups or religious zealots or thieves or adorable little girls who have begun to show signs of demonic possession. You can have a tech bay where dune buggies get machine guns welded to them and leather jackets get metal plates sewn in and everything gets a kickass skull painted on it. You have room to build characters in the safe havens, but can still dispatch endless redshirts in nighttime sorties.

Enough tangential ramblin's, here's my answer to your question: I'd get involved in training and education. There'd be a big job to do, compiling and cross-checking data about our current situation and the nature and strength of the abominations. Communications with other safe havens would have to be established and maintained and we'd have to put together a solid plan for acquiring and managing resources of all types. People would have to know how to operate to avoid death or mutation, fighters would need to be skilled and efficient, not wasting our ammo supply or getting hurt unnecessarily. We'd need a corps of skilled workers to handle medicine, water management, equipment construction and maintenance, food production and preservation, all the stuff. The nuts and bolts of running a post-apocalyptic society would be like playing Dwarf Fortress with a really good texture pack, and it would be fun and rewarding to talk to other administrators, discover our needs, orchestrate missions to collect them, and generally XCom the whole thing. Plus, you rarely get eaten by interdimensional hellbeasts when you're working behind a desk, unless you do a really, really bad job.

I would first start by gathering weapons, I don't own a gun, so checking nearby neighbours would be a good idea between zombies mutants and humans who just want to kill others, they would be more of a danger then initially running out of food and water

Id also try to gather a group of people, perhaps a bus for carrying them

Before heading to somewhere more remote I would gather other supplies, solar panels would be good, half the houses in the neighbourhood have them, I have a Ute for loading them on, a decent source of energy and petrol will not last for long, tools, my work has allot of tools and repair supplies, so assuming all the chemicals didn't catch fire and blow the place up it would be a good place to raid, and its near a few supermarket distributor warehouses, so there should be ways of getting a truck, and loading it with pallets of food/supplies, most people i think would head for the local supermarket, which would be to dangerous (also where library usually are as well, so id skip them)

The city would be to dangerous to stay for long, so after gathering everything to last until a safe location and getting settled, not sure where after that, assuming that I have a group, then it would likely be a group decision, my leaning for somewhere remote, with a large pool of water perhaps a natural dam that we can then fortify against roaming bandits

I think it would be best to be quick. get everything and get out of there, before someone with more force is able to gather and take the supplies from you.