Whoever does not fast some days of Ramadan has to make up those days before the next Ramadan comes. For more, please see the detailed answer.

The Du`a ‘Allahumma laka sumtu was ‘ala rizqika aftartu’ is narrated in an inauthentic Hadith. There is no source for the Du`a ‘Ashhadu an la ilaha ill-Allah astaghfir Allah as’aluka al-jannah wa a’udhu bika min an-nar.’ The reported Du`a when breaking the fast is ‘Dhahaba ath-Thama’u, wa abtallat al-`urooq wa thabata al-ajr insha Allah.’

There is no specific Du`a for Ghusl, but it is desirable to say Bismillah when beginning the Ghusl.

We do not know of any specific Du`a in the Sunnah for protecting a traveller until he returns to his family safe and sound.