Do the stock CDI boxes just suddenly fail ??

[Bill Hilly]

I see a lot of post on CDI boxes, and I was wondering if the stock ones just suddenly fail with no warning, or are there warning signs ? I take long rides way out in rural areas that the houses are few, and far between, and there is often little to no traffic on the roads. I carry gas, and some tools, as well as the stock plug with me, and I need to carry flat tire stuff, but is a spare CDI ,just to carry a good idea??
Thanks