my $cgi = new CGI::Applicaton(...);
$::global_var = $cgi;
... use $::global_var now anywhere ...

##</code><code>##

...
{
  package main;
  our $global_var; # same as $::global_var and $main::global_var
  ...
}

##</code><code>##

print $hash{'key'}    # same as print $webapp->param('key')
$hash{'key'} = 3;     # same as $webapp->param('key', 3);

##</code><code>##

our %hash;
my @all_params = $webapp->param();
for my $p (@all_params) {
  $hash{$p} = $webapp->param($p); #
}
... use %hash instead of calling $webapp->param(...) ...