This turns sub1 and sub2 into closures (see 'What's a closure?'). While it is not always necessary to use BEGIN blocks, without them (i.e. normal blocks), declaration order becomes significant.

Update: A trick I use occasionally is to declare a set of lexical variables in a BEGIN block along with access functions. Within the program, only the access functions are visible.

BEGIN {
  my ($var1, $var2, $var3);
  my @array1;
  my %hash1;

  sub var1 { $var1 = $_[0] if @_; $var1 }
  sub var2 { $var2 = $_[0] if @_; $var2 }
  sub var3 { $var3 = $_[0] if @_; $var3 }

  # for arrays and hashes, call in scalar context and
  # dereference to manipulate contents
  sub array1 { wantarray ? @array1 : \@array1 }
  sub hash1 { wantarray ? %hash1 : \%hash1 }
}
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Of course, rather than hand code access functions for every variable, I typically define a hash containing my variables as keys, and an AUTOLOAD to define access functions dynamically on first use.

dmm