Have a good journey!
'Viaggio' — VIA-gio. The 'ggio' sounds like 'jo'. Stress on the first syllable. 'Buon' — BUO-n (final 'n' is not strongly pronounced).
Use when someone is departing for a journey — by car, train, plane, or any travel. One of the warmest and most used Italian departure wishes.
'Buon viaggio' (good journey) is the standard Italian farewell for travelers. It combines 'buono' (good — elided to 'buon' before consonants) with 'viaggio' (journey/travel). The whole 'buon + noun' construction creates wellwishes for specific activities.
Buon rientro!
Safe return! / Have a good journey back!
'Rientro' (return home) — said when someone is returning rather than departing
Viaggia bene!
Travel well!
Imperative — more active, wishes good travel experience rather than just a good journey
Arrivi sano/a e salvo/a!
Arrive safe and sound!
'Sano e salvo' (safe and sound) — classical expression for wishing safe arrival
Italian families have a strong tradition of following travellers with wellwishes and requests for updates on arrival ('fammelo sapere quando arrivi' — let me know when you arrive). This is an expression of love, not anxiety. Not sending an arrival message is considered inconsiderate.