Since starting my minimalistic lifestyle, I've tried not to spend a lot of money on frivolous things and most of the time I am successful at it. Recently, my mom came into town and visited me and usually when she and I get together, we spend like there's no tomorrow. I spent about $90 over the course of a few days and some of the things I bought, I didn't even need and now regret buying. When I realized I had lost my self-control over the items I was buying, I tried to figure out what was enabling me to do so, and really it was because I had the money available. And then I began thinking about how I could stop myself from wasting money and was hit with this new rule.
The $20 rule
The '$20 Rule,' is something I decided to implement in my life to prevent me from overspending. As of right now, I have a card that works as both a debit and credit card and is what I use to buy most things. If I set my limits and make sure I only use that card to buy the bare necessities (food and clothes) or whatever I'm going to the store with the intent to buy (groceries and other odd items for around the house), then I allow myself $20 in cash in my wallet. The $20 is there for the trinkets that I see and want to buy. In this way, even if I do waste the money, it's only $20.
The $20 rule in the long run
The $20 that you set to the side for your impulse buying should last you a month if you're being smart about your choices. You should ask yourself if you really need it, how long you'd use it, is it really worth the price you're about to pay, etc. The longer you think about it, the easier the choice should be as to whether you can afford to buy it or not, and if you're spending too much time deciding, it means you definitely don't need it.
Don't let the $20 carry over to the next month. If you still have $20 left in February, you shouldn't allow yourself $40 for the month of March. There should never be more than $20 in cash in your wallet at once (unless you know you're going to an event where only cash is taken). You should never replenish the money before the month is over. So if you spent $10 within the first week of the month, you only have $10 for the rest of the month to spend. If you don't spend the remaining $10, then you may add more money to have the full $20 back.
Why it works
Although I've just started this trick, I know it will help me in the long run because I'm setting a set limit on myself on what I can and can't buy. A lot of my personal impulse shopping is done because in the back of my mind, I know I have other money somewhere else that will cover me if I waste a few dollars here and there. Yes, this is a terrible mindset to have because you can easily lose a lot of your money by thinking you always have a backup plan. This rule allows me room to still buy the items I don't really need but would really want, and at the same time doesn't give me complete access to splurge it all in one place. By having a limit, I am forced to really think about what's important to me and what I would actually use in the long run. Spending those extra few moments to consider whether an item is worth buying or not will save you more money and will help develop your self-discipline skills by forcing you to control your impulse shopping.