Like many, I use a module (docs, Dean::Util), however it also has the ability to remove dependency on itself from scripts and other modules. For example:

# In some script/module
use Dean::Util qw/map_pair nsign min_max/;
# other code ...
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Then later to send the script to other machines:

perl -MDean::Util -we insert_Dean_Util_functions the_script.pl
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This replaces the use Dean::Util line with the code for the subs requested (and optionally documentation). The insert_Dean_Util_functions function is a bit of a kludge, but it works.

This gives the benefits of using a module (old code uses improved functions when I get a chance to fix up code in the module) as well as the benefits of copy-paste (can transfer scripts to other machines without installing my module).