For pets on regular medication, pack enough to cover the full trip plus a few spare days as a buffer against delays, all kept in its original labelled packaging rather than repackaged into travel containers. A printed summary — ideally a formal vet note — of a pet's medical conditions and current prescriptions is genuinely useful to have on hand, and becomes especially important for any medication classified as a controlled substance, where customs or border staff may ask for documentation.
A bilingual note — English and Italian — makes this far more useful in practice, since not every vet clinic outside major cities will have an English speaker on staff. Italian pharmacies (farmacie) stock basic over-the-counter items, but prescription pet medication should come from a vet clinic rather than a corner pharmacy.