Expression: I'll cross that bridge when I come to it.

When you have a possible future problem or decision, you may prefer to wait to think about it, solve it, or decide, until it actually happens. In this case, you can say, "I'll cross that bridge when I come to it."
A few examples:
"What will you do if they offer you the job in Bhutan?"
"I don't know; I'll cross that bridge when I come to it."
"What if our customers don't like our new product?"
"Well, let's cross that bridge when we come to it."

P.S. This post is dedicated to Montse, who reminded me of this wonderful expression!