my %hash = (
   word => 1,
   second => 3,
   third => 7
);

######

my @weighted = ();
for %hash.keys -> $key {
   push @weighted, ( $key ) xx %hash{ $key };
}
say @weighted.pick;

###### Basically the same thing:

my @weighted = ();
push @weighted, ( $_ ) xx %hash{ $_ } for %hash.keys;
say @weighted.pick;

###### One-liner style.  *Somewhat* based on Roger's above.

%hash
   .keys
   .map:{
      ( $_ ) xx %hash{ $_ }
   }
   .pick
   .say;

## (or actually on one line)

%hash.keys.map:{ ( $_ ) xx %hash{ $_ } }.pick.say;