I would consider a just-in-case poncho in an area where the rain is pleasantly warm (and occasional).

In my area, where the rain is cold, it's a recipe for trouble (or at least, a fair degree of nuisance and/or misery).

Here's a thought: when I was a poor student backpacking in the backcountry, I would add the "Colin Fletcher trash bag kilt" when the rain socked in. This really made a difference in keeping my legs dry, but still well ventilated. More importantly, it kept my socks and the inside of my boots dry. I vaguely recall using first-aid tape to create a crude rain gutter, front and back, that drained the worst of the water to the sides instead of onto my legs. This concept could be applied in a whole lot of places.