Convince yourself that you don't have any. If your broke you can't spend. Put petty cash aside and let it grow instead of using it. It's much nicer to have a couple hundred than to have 15 or say 25 dollars and think you just have to have something "cute to spend it on right there in the moment. Self control..... Have some and you'll have more money for bigger and better things.
Simple math! Make yourself a monthly budget of a total of all your expenses and how much income you receive each month. Set aside money from each paycheck to cover 35% of your monthly bills and spend the leftover money wisely! If you can't afford to buy something with cash, you cannot afford it. Good luck!
Pay yourself $10 per day, put that money in an interest-bearing savings account! You'll be surprised at how much you've saved in a short time! Have it taken out of your paycheck each week, you'll never miss it! That's $70 per week and it adds up quickly! You're going to be richer than before.