Instead of telling yourself "no" all the time and living in fear of your debit card, say "yes", but with a plan.

Calculate how much you can really afford to spend each pay period on snacks, energy drinks, coffees, and impulse purchases. Take that amount and put it onto a prepaid visa card. Carry that with you to work and you'll know how much you can spend. If you spend it all the first week, you'll have to bring from home for the rest of the time.

Every few paychecks, put a little less on the card until you come to a point where it feels like you are treating yourself instead of depriving yourself. Come up with alternatives for the other days. Skip a day, bring something from home, etc. Put the difference from your original deposits and the new amount on a second prepaid card. Let the extra build up on that card for a really good "treat"--a new outfit, taking your boyfriend out to eat, whatever you want to save for. You won't feel like you are depriving yourself of your daily energy drink when you remember what the other card is building up to.

Your "treat" money will be on the card and you shouldn't have to have your boyfriend hide your checkbook and debit card. Just keep reminding yourself you have use the treat card only.

My husband and I are both on an allowance.  This is money we can each spend on whatever - no guilt, no questions.  The amount has changed over time depending on what our finances look like, but we started this system when we were watching our money very closely and absolutely had to make sure we did not overspend.  It works, so we kept at it.  Even though we have more money now and could be looser with our finances, we still maintain the allowance strategy because it keeps us from frittering away our money on little stuff. 

I don't keep extra money in my checking account, so I can't overspend without overdrawing my account.  We have a budget and we put the agreed upon amount in savings right off the top - before any bills are paid or any money spent on anything.  Then we pay the bills and so the only thing that is left over is spending money.  If I want to buy something that I can't afford with my allowance, I have to make a concious decision to take money out of savings to do it.