"Rain or shine" is a common phrase that indicates that an event or activity will take place regardless of weather conditions. However, there are other expressions that can be used to convey the same meaning, such as "come hell or high water," which emphasizes the determination to follow through with plans no matter what obstacles arise. Another synonym for "rain or shine" is "come rain, come shine," which focuses more on the idea that the event or activity is happening regardless of external factors. "Come what may" is yet another option, which implies a commitment to sticking to plans even if it means facing challenges.