I am dependent on glasses too. Sometimes when least expected a lense will decide to leave the frame and I find myself trying to fix them while I am half blind. I tried several approaches like having several real cheap glasses around me to use for those critical few minutes.
Maybe I should put a spare pair in the car, but it can happen when I am not in the car. And it is near impossible to carry the spare all time.
Also, having one pair for driving and one for reading complicates things. So, maybe I should have a bifocal, lower half of the lense for close-work trying to fix the original broken pair, and the upper half of the lense for driving back home if I lose the screws or it is too dark to see and fix anything.