use strict;
use warnings;
use Tk;

my %w;

$w{mw} = MainWindow->new;

for (qw/ this that a_longer_name X /){
    my $bttn = $w{mw}->Button(
        -text     => "$_ ",
        -font     => 'times 19',
        -justify  => 'right',
        -compound => 'right',
        -bitmap   => 'warning',
       #-image    => $w{mw}->Photo( -file => 'whatever' ),
        -anchor   => 'e',
        -padx     => 4,
    )->pack;
    push @{$w{buttons}}, $bttn;
}

$w{mw}->update;

{
    my $width = 0;
    for (@{$w{buttons}}) {
        $width = $_->width if $_->width > $width;
    }
    for (@{$w{buttons}}) {
        $_->configure( -width => $width );
    }
}

MainLoop;