I think writing down the day's spending at the end of every day is the place to start.
Just as simple as:
3/17 Gas $20
Lunch $11.50
Bottle H20 $1.09
3/18 Newspaper $0.27
Candy bar $0.67
Iced Tea $1.32
For me, this works better than just stuffing the receipts in an envelope b/c it actually forces me to stop and consider what I've spent that very day. If you haven't been keeping track, you will likely be SHOCKED at how quickly the pennies and dollars add up. What I used to spend in a month at Starbucks would give me a heart attack now--but b/c I wasn't adding it up, it only seemed like a few bucks here and there. And truly, it was. But that adds up!!
Anyway, at the end of a week or month you can categorize things as you like and sum up the total spending. From there, you can decide what is reasonable and what is too much.
At the beginning of the next week or month you can set those goals: like $30 for eating out/snacks; $150 for gas; etc.
Then as you go, you can tally along like $14.23/$30 for eating out. The first number is where you are and the second is the max you'll spend. Or you can set up some sort of Excel worksheet that will auto deduct as you enter the figures. Or do it by hand. Or whatever.
But there is a max and you will adhere to it (barring some emergency or miscalculation of what your normal spending is). And at any given point, you can quickly figure out that you've got $7.18 left for snacks....or whatever....and decide from there if the $4 coffee is in the budget and/or worth it based on what you've got left to spend for the month.
I've found the No Spend Challenge thread to be an awesome way to track my spending and be accountable--just to myself! So you might want to join or lurk there.
