Well again, that depends on what you want to do with the machine, next to DNS. If it's only DNS and no mail or websites, you can disable almost all services except the named/bind service. So you could disable FTP, Exim, Dovecot, Apache, php-fpm, da-popb4smtp.
Maybe also Mysql/MariaDB but I'm not sure about that.
You might need to keep Exim for system messages and pure-ftpd if you want to still be possible to login via ftp.