"Just in case" should be cheap if not free, not something you have to pay for regularly
Consider the following...
1. I need an unlimited talk, text and data plan JUST IN CASE I need it.
2. I buy a bigger car JUST IN CASE I need to pick up some dry wall from Home Depot and to take some friends around town when they visit me
Do we really need to pay for JUST IN CASE for the JUST IN CASE?
How many people do the above? My idea is that as long as the things we need are available, even at a higher one-time cost, would be better than paying for it regularly.
For the cell phone example above, on average if one talks on the cell phone for 700 minutes a month and he have a choice between a 900 minutes-a-month plan or an unlimited plan, a lot of people would opt for unlimited because they want the ability to talk more JUST IN CASE they actually need to talk more. If you look at the price differences between the two plans you will likely fine them at about $10 - $20 per month more for the unlimited if not more.
But don't forget, if your average usage is about 700 minutes, you have 200 minutes to spare before going over the limited, and each minute you go over can cost you anywhere between 10 cents to 30 cents per minutes. How many minutes do you have to "go over" to reach $10 per months? AND, how often do you go over? Once a year, twice, may be three times? As long as your answer is NOT more than six, you should not opt for the unlimited plan because you are paying for it every month.
Similarly for the bigger car, you can rent a van or truck ONLY when you need it, not something you are stuck with (and pay for) for a long time.
Just some thoughts.