Hanami picnics are common, but Tokyo parks have strict rules: no music, no fires, no excessive drinking. Trash must be carried home.
Tarps are used to mark space. Don't disturb others' setups — Japanese hanami is communal but personal-space-respecting.
Ueno Park is the loudest hanami site. Shinjuku Gyoen requires a small entry fee and bans alcohol entirely (calmer).