I came home one day early just in case my flight got delayed.
I decided to come home a day ahead of my original plans in case my flight got delayed for some strange reason.
この場合、次のような言い方ができます。
ーI came home one day early just in case my flight got delayed.
「万が一飛行機が遅れた時のため、1日早く帰ってきた」
just in case で「万が一のため」
ーI decided to come home a day ahead of my original plans in case my flight got delayed for some strange reason.
「万が一何らかの理由で飛行機が遅れた時のため、元々の予定より1日早く帰ることにした」
ご参考まで！
カナダ 
