I try to spend around $600/mth on food, gas, drinks and other entertainment. This works out to roughly $20/day. I keep a running tally in my head day to day on what I've spent and try to stay around $20/day. This is not a great tracking method, but just having the idea of $20/day in the back of my head curbs my spending a great deal.
I wrote up my system in another thread - I do almost exactly the same thing, except it's $40 a day for me, my wife and 2 kids. The only difference is we actually "pay out" the money each day, and only spend from what we've accumulated from that day and previous days.
I really like that way of keeping a running tally.