I don’t have one personally, but here are a few ones recommended historically:
1) the Yerushalmi says that one should always have on one’s lips the phrase from Tehillim, “Lord of Hosts, happy is the man who trusts in you.”
2) “Gamzu l’tovah,” as mentioned in Talmud Bavli in the story of Nachum Gamzu.
3) The Shulchan Aruch rules that one should always be in the habit of saying, “Everything the Merciful One does is for the good.”
4) Rebbe Nachman of Breslov recommended that people repeat the phrase “Ribbono shel olam,” when they find themselves unable to practice hisbodedus in his preferred sense of talking to Hashem in your own words.