I'll probably have to wait about 5 days before Sam's Club can get the replacement tire I need. How safe is it to run errands with the "donut"
(rear right wheel)?

You should be fine if you keep the speed down. Check for yourself but I think the donuts are good for 50mph.

Many thanks for your prompt reply!

To other interested readers, I want to emphasize that front-wheel drive cars really don't like to have the donut as a front wheel. Smaller circumference, etc. Unless you will only make a very short trip, make the extra effort to swap it to a rear position.

In all cases, make sure the donut is inflated to whatever the sidewall says. Probably 60 psi. Standard, speed, braking, and cornering precautions.

DAS (donut-hater)

Thanks, tochatihu,for the useful info! Jan