When we visited Italy a few years ago, it was April, and the forecast was sunny and warm. On our first evening in Rome, a hugely torrential downpour soaked us to the bone and postponed some of our sightseeing. We hadn’t anticipated rain, so we didn’t bring our packable rain jackets. We haven’t made that mistake since. Most people find it challenging to pack their rain jackets in a suitcase or backpack. But a truly packable rain jacket is small enough to fit in the tiny pocket of your backpack or purse. Choosing the right jacket depends on...