That seems easy enough. A first approach with a for-loop might look like this

sub seq1 {
    my $r;
    my $r0;
    my @R;
    for my $c (split '', shift) {
        unless (defined $r) {
            $r = $c;
            $r0 = $c;
        } elsif($c eq $r0) {
            $r .= $c;
        } else {
            push @R, $r;
            $r = $c;
            $r0 = $c;
        }
    }
    push @R, $r if length $r;
    @R;
}
[download]

But what is with Perl's promise of "simple things easy"?

Let's look at bigger shells then: Regexes:

sub seq2 {
    my @x = shift =~ m/((.)\2*)/g;
    map $x[2*$_], 0..@x/2-1;
}
[download]

The 1st line is actually mine, while credit for the 2nd goes to murphy on the German perl-community board, fixing an oversight by me.

This looks quite good, and Benchmark even suggests, that it has a little edge in performance over the for-driven sub.

Alas! it would be perfect, if no postprocessing was necessary on the match expression result!

Oh enlighted monks, is any such "easy expression for the simple problem" laid down in your holy books?

Footnote: granted that readability and elegance are to a great extend functions of individual perception, I was nonetheless frustrated that I could not dig up an "elegant" 1-liner for the described problem so far.