So, you wake up one day and find that you're the only person left in the world. Kind of cool, right? No obligations, no rules, no limits. Go for the exotic fruits first. If your mangos and bananas are imported from overseas, chances are they'll be hard to come by. So eat them while you can and enjoy every last bite.
You might think that with no one stopping you, you could go anywhere! But not so fast! All those abandoned cars, boats and planes you see lying around will be useless in about 2 years when their fuel goes stale. Guess you'll be sticking around. But for how long? If water, food, and shelter are your basic needs, shelter would be the easiest to come by. You'd literally have a world of homes to choose from! But be careful where you settle down.
Cities would become dangerous, since without proper maintenance, they'd start to fall apart pretty quickly. Nature's elements: rain, frost, and heat, would take their toll. Rot and mold would become widespread, and vegetation would crack through concrete and break through glass. But even if you were to fight back against nature's reclamation of the land, all it takes is one bolt of lightning to start a city-wide fire. And you can't call the fire department. So run for the hills! But even the country isn't all that safe.
First of all, there are predators you'd need to defend against. Wild dogs, feral cats... bears...But you'd only have to worry about them as long as you could still breathe. There are more than 400 nuclear power plants in the world. And once their automated safety systems began to fail without human supervision, there would be meltdowns across the planet, rendering many regions simply uninhabitable. In terms of food, the city would be your best bet. Supermarkets have enough canned and frozen food to last you for decades! Whereas in the country, crops and livestock would start to dwindle without proper care or protection from predators. But if natural is more your style, you'd have to go back to the old ways of hunting with a spear or a bow, since ammunition would be limited and harder to come by.
Maybe you could grow your own little vegetable garden, but that would cut into your water resources. Without other humans, you'd be without electricity. Water pumping stations and treatment works would shut down, and the fresh water kept in reservoirs would go stale quite quickly. You could rely on bottled water, and you'd probably have thousands of litres to go through, but eventually, you'd have to learn how to purify your own. You'd have to teach yourself a lot of things, but lucky for you, you've got a lot of time on your hands, and millions of books out there with all the information you'd need to survive effectively on your own.
So, while it might be hard at first, you could technically survive as the last human on Earth. But would you really want to? Humans evolved together as social creatures in order to survive. We joined forces against hunger and harsh weather; and built families and communities to share stories, empathize, and keep each other happy and healthy. Human contact has been scientifically proven to build trust and reduce stress. So, while it's apt to cramp your style, be glad it's a small world, we need each other more than you think!