That's exactly how I've been using it!
Since my life style is driving my car everyday in suburb city = I just grab this little key pouch only and go for a quick errand when I don't need to carry a bag, example to go to lunch or Starbucks, and go to grocery and drop off my car at the wash service or drop off my pets at pet salon. It was also so handy when I dropped off and picked up my kids from school in the past ( my kids are grown now )
I've been using only this key pouch for these kinds errands daily and such a smart little thing in my life. I think it is the best for a daily car user like me.
I also use my mini pochettes or PAs in both mono and DE in my larger bags. I agree either are very useful SLG as many members mentioned as well