I am also retired... but my wife is still employed.

Many of the normal errands I run... I accomplish by bicycle (weather permitting). The post office, the bank, sure. Maybe more importantly... an occasional trip to Starbucks or to the gas station to buy a lottery ticket. We still own two cars but only drive about 6K miles combined.

My old (2010) road bike has become my back-up/spare/rain bike. It has campus pedals so cycling shoes or tennis shoes work fine. I just added a mirror the other day so I can ride without my contact lens and cycling glasses (that have an attached mirror). It also has a rear rack with a trunk bag. No it won't haul groceries... but mail and a check book are fine... not to mention a jacket and tire repair tools.

I'd try the 2nd bike... one car route. I've thought about this same idea for when my wife retires.