Saving for replacement and maintenance

One of the areas of budgeting that I'm completely ignoring right now is saving continually for the replacement and maintenance of our stuff.  You know, car repair budget, furniture replacement budget, appliance replacement budget etc.  So far we've just had enough money each month to cover these expenses as they arise.  And we're really not that into keeping our household goods in tip top shape either.  Our couches are all scratched up from the cat and our rooms emit that "lived-in" feel.

But this won't work forever and truthfully I have no idea how much I should be setting aside each month to save for these inevitable expenses.  $50?  $100? More?  How can I even guess?  Trips are easier.  If I know where I want to go, how long I plan to stay and roughly what activities will happen, I can guesstimate the expense, divide it up by the months until the trip and save accordingly.

The problem is I don't know when my television will kick the bucket.  It could be tomorrow, it could be in five years.  We also don't know when one of our cars will die or need major repairs.  But in the case of a car we at least have a plan.  My car has many more miles on it than my husband's car so it is likely my car will be retired from service first.  If that happens before we're out of debt we'll put the snowball on hold and save until we have $10,000 and I'll buy a car, all the while sharing with GJS.  We carpool anyway so it wouldn't be much of a challenge, more a slight inconvenience from time to time.

I'm on a mission to figure this out, or at least to find a quasi-reliable guide for how to save for these things.  Thus far I have not run across this information.  If you have seen a system or have a program in place for this please let me know.  All ideas are welcome!