You can't get there from here

Trading

The problem is with this line:

          for my $cargo (all_selections($items)) {

As @$items gets larger, the number of possible selections gets large very fast

        Number of items             Number of cargoes

          1                                  1
          2                                  3
          3                                  7
          4                                 15

         10                              1,023
         15                             32,767
         20                          1,048,575

         30                      1,073,741,823

        100        1,267,650,600,228,229,401,496,703,205,375

For n items, this algorithm takes time proportional to 2ⁿ