use DDS;

# your $events structure here ...

@$events = sort { $a->{month} <=> $b->{month} } @$events;
@{$_->{list}} = sort { $a->{date} <=> $b->{date} } @{$_->{list}}
  for @$events;

Dump $events;

__output__

$ARRAY1 = [
            {
              list  => [
                         {
                           date => 10,
                           name => 'picnic'
                         },
                         {
                           date => 15,
                           name => 'high tea'
                         },
                         {
                           date => 23,
                           name => 'rafting'
                         }
                       ],
              month => 7,
              name  => 'July'
            },
            {
              list  => [
                         {
                           date => 12,
                           name => 'golfing'
                         },
                         {
                           date => 20,
                           name => 'retreat'
                         },
                         {
                           date => 29,
                           name => 'marathon'
                         }
                       ],
              month => 8,
              name  => 'August'
            }
          ];