Get my best friends and family, some canned stuff, survival equipment and weapons (both dull and firearms) and make my way upstream to the stream of the river. This way I have fresh water solved. Then if it's a mountain (no clue where my city river comes from) there's also animals and we can hunt and eat berries. If it's a hill, then we can plant stuff and eat it. Also have a radio with us so when they relaunch stuff we'd hear it.