To do this in a way that doesn't export package vars as well (which I believe was davorg's objection), perhaps this would work:

@EXPORT_OK = grep {defined *{$MyPackage::{$_}}{CODE} }
                  keys %MyPackage::;
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And unless I'm very much mistaken, that line could just as well be at the top of your package as at the bottom: unless you're doing fancy run-time redefinition of subs, they should all be defined by the time the first line of non-begin-block code gets evaluated.