My emergency umbrella is a small beach umbrella large enough to cover me,plus the dog who doesn't like raindrops in her eyes. I keep this by the back door, handy if needed to take her out when a morning is too wet for her taste.
We have two golf umbrellas in the van and possibly the folding umbrella, none of which are in reach if showers break out while we're IN the van.
My mobility scooter has no umbrella onboard, but it does have a straw tennis brim to keep rain out of my eyes when I'm riding it, or to hold the water-shedding, onboard poncho's hood from blowing off my head in heavy rain.
I have a space blanket onboard, in case the scooter battery dies when I'm far from shelter as a cold night falls. But it would be better to have a motorized umbrella, to fly awaaaaayyyyy.....