I'd also put "Wot If..." questions on people's property in paint. Other than that, I'd stay at home and watch Rosario x Vampire, Azumanga Daioh, the like.
Probably find as much can food as possible and collect rain water. I can't run a city by myself, but I guess I can at least do those things to survive. Chances are, the 1% remaining would be far away as I live on an island.
Maybe try read some books on certain things if I want to figure out to make something function or whatever.
....For a less serious answer, I guess just breed mice and have it rampage the entire city.
Probably be a bit sad considering it's a good chance all of my friends and family would have disappeared overnight. While grieving I'll look to gather supplies and I'll set up traps (Of any kind to stop scavengers/thieves) Probably live out my entire life like that because it's unlikely I'll come in contact with other people depending on where the population would be concentrated.
