happiness = things_you_have - things_you_want
It's much easier to reduce your desires than it is to buy new stuff. Your resources are scarce and your desires infinite. If you can convince yourself you have everything you want already nothing can touch you. Write down a list of reasons to not buy the new hotness.
Stoicism has more to say on this, for example negative visualization. If you feel upset with your spouse or kids imagine them being hit by a car and dying in your arms. Car or truck? Did the car stop, or speed off? Burial or cremation? What will you say to your family, their friends? Manufacture details and explore their emotional impact. The frustration just evaporates.