I'm guilty of impulse shopping also.
Related to live fish, what works for me, is the thinking of how bad they take care of the tanks at the big chain stores (and some LFS
also), and I just think in the high chance of introducing a parasite, or bacteria to my tank!!!. That feeling stops me from buying live fish most of the time. Buying online is the way to go (IMO
But regarding hardware, I'm hopeless, I still purchase by impulse!!