Which is fine!
Here's what you do: allot a certain amount of cash to discretionary expenses each month. You take that money out at the beginning of each month (actually in my case, twice a month) and then use it. And when you run out you're out.
What you've just done is used physical cash to put a hard ceiling on your discretionary spending. This turns what are normally variable expenses into a fixed item in your budget, which makes it a heck of a lot easier to account for.