Weather in Cascais in October

According to Accuweather's historic average for Cascais, the low is 12 Celsius (54 F) and the high is 18 (64 F).
Of course, it's best to check the predicted forecast shortly before departure, because we all know it's highly variable these days.
For example, here's the 10-day Forecast on the Weather Channel, or you can use whatever weather site you prefer.

According to first-hand reports, as well as a site called Holiday Weather (which I've never seen before), Lisbon averages 11 days of rain in October and November.

Probably it's from living in Seattle, but I always pack a rainjacket (helpful for wind too) and sometimes a small umbrella.

On the other hand, it may be warm and sunny, so I'm also going to pack a sunhat and even sunscreen (because my skin is sensitive to the sun).