designated Shabbos suit
my best tie, which i wear only on Shabbos
shine my shoes
belt with gold buckle instead of weekday silver buckle
better hat
but the ikar of Shabbos begadim is not necessarily better or nicer, although that is certainly appropriate and a hiddur.
but the ikar is to have begadim that are designated (miyuchad) for Shabbos and Shabbos only.