In my editor I have a macro that inserts:

#! perl -slw
use strict;
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And that's how I start all my new Perl scripts. Anything else gets added as and when I need it.

On the other hand, in my REPL, which is where I do the majority of my trail&error coding, I have a bunch of things including:

use threads;
use threads::shared;
use Data::Dump qw[ pp ];
use List::Util qw[ min max sum reduce ];
use LWP::Simple;
use XML::Simple;
use GD;
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It also has a bunch of small subs that I use commonly: rgb2n(), n2rgb(), uniq(), rndStr() and others. But both lists tend to change as I encounter different requirements.

I also experimented with use 5.010 (for say) for a little while, but I still use a 32-bit perl5.8.9 sufficiently frequently (because more of CPAN is available via PPM for that build than my 64-bit 5.10 installation), but the inability to use scripts that contain 5.010 with that build put me off.