I live in a mostly temperate zone that occasionally has freezing rain. What can I use for an improvised ice scraper from items in my car or on my person for those times when I am away overnight from home out in the country? A credit card won't work for frozen rain, it only works for frost.
If you have a CD player in your car, chances are you have some old CDs laying around. You can use those (or leave a blank CD in your car) to scrape ice from your windshield.
CDs - Do you still listen to that summer mix you made 15 years ago? If so, put the music on your computer and use the CD to clear your windshield! This method works best for a thick layer of ice.
Source. The above-quoted website also suggests leaving a stiff, plastic spatula in your car, although admittedly you are unlikely to have a spare spatula laying around in your car.
Of the things you are likely to have on you or in the car... you can use neat windscreen wash fluid if you happen to keep it in the boot/ trunk / glove compartment. A credit card will work but you have to hold it very close to the working edge and it's hard work... and it's likely to destroy the card. Don't use vehicle antifreeze, it risks damage to the paintwork.
Possibly you have spirits with you... some people do consider it a vital thing to carry. Vodka will work well to melt ice, it's just a very expensive way to defrost a car!
Or of course you can be prepared... leave an ice scraper in a door pocket for just this sort of eventuality. It can stay there until you need it, it can change cars with you.