personally i would be trapping and hunting in the big cities.
realistically, how many people who live in cities would have the first idea of how to survive? barely any, and those who do (like members on here) would all be down the beach eating 700 limpets a day, while the foxes and pigeons re-claim the cities and arent hunted because barely anyone in a city would know how.
Foxes and pigeons can only sustain themselves due to humans being there. No humans = no waste = no animals.
You'd still have your rivers/water systems though.