This product (I've not tried them, but want to) might prove very useful in your BOB and general prepper stock.
The idea is to make a single pair of eye glasses which can be adjusted for different magnification.
The full article is a short user reply to a reader question:
https://survivalblog.com/odds-n-sods-1034/The article contains four links to different sources. One link, the second in the list, does not work from the website. The correct URL is here:
http://www.firststreetonline.com/Healthy+Living/Vision+Solutions/Hi+Powered+Adjustable+Readers.axdDO READ the various user comments on these products, some have drawbacks (hard to read, headaches, etc.) But in a pinch, you may need to replace your glasses or provide a replacement to one of your group...