Wiktionary
impulse buying
n. the act of making unplanned or otherwise spontaneous purchases
Usage examples of "impulse buying".
Handouts to every loser who comes whining to her with a pathetic story, contributions to causes like 'Save the Oysters,' impulse buying on a level you can't begin to imagine.
Normally, she would never have given in to impulse buying, especially not from anyone as disreputable as a star base street vendor, but the painting seemed to her to be a sign.