Don't discount the fishhooks for urban use. If you find yourself homeless you can fish for duck, pigeon and squirrel easily enough with some bread or popcorn as bait. Make sure to use some strong leader tho. If you use steal leader it cannot be shiny. Box traps are usually easier but more conspicuous in the park. The piece of popcorn attached to the end of a handline can be twitched under a bush and no-one will know it's there until the squirrel starts raising a ruckus - then simply step on the little bugger and pocket dinner until you have the time and privacy to flesh him out. Little beats fat, nicely corn-fed, squirrell but it disturbs the locals to see you harvesting them.