Zero last year and 2 this year.
But, I find that my time is worth far more to me than the cost of an extra tube. And it takes longer to patch a tube than to simply replace it.
I do carry a patch kit with me in the unlikely event I puncture my spare tube that I carry. But if I don't, I throw the old tube away and order a new one when I get home.
An even better option is to go tubeless. Then no worry at all about tubes. I did it on my mountain bike and am thinking about it on the road bike.