My Dad's old medical partner bought in bulk. He was always terrified that items he loved would become discontinued, and when they wore out he wouldn't get them again. He's most famously known around town for buying literally 100 pairs of the same stupid leather moccassins. So he has literally a lifetime supply of them.
Too many times I have found a product to be clearly superior and thought to myself that surely it would catch on and that its outstanding qualities would guarantee that it would remain in production and available. Only to come back later wanting another, sometimes after the first example wore out, only to find out that the design is no longer made. Often that the company that made it had been bought out by some mindless conglomerate that is only interested in manufacturing vastly inferior copies.
If I find a design I really like after sufficient use to show its virtues I often make a point of going back and buy more. Unfortunately the pace of acquisitions and mergers is such, and production runs so short, that often I find what I like to be a virtual one-off. If you find something you like, something you really like, something clearly superior in price, quality or value, buy more of them.
I would add a reassurance and a warning. The internet, and presence of sites like E-bay, means there is less chance you will get stuck with stuff. Used to be a person who stocked up on a specialty item was taking a risk. Yes, there were others out there who might want, even need, the item, but there were few ways of contacting them.
A friend rebuilt antique foreign cars as a hobby. A dealership went out of business in the 70s and he bought their entire stock of specialty tools. From the mid-70s to the mid-90s he only sold a few. There were people who needed and wanted them. But few ways of telling any of them you had what they wanted. When he got online he got into news groups and sold the tools by the hundred.
Lesson here is that if you find something good there is likely someone who would agree. If you bought it at a good price, and you don't get greedy, you will likely be able to sell what you can't use. The market is world-wide and most of seven billion strong. Odds are there are hundreds of people who share your interests and preferences.
The one major exception is, with a few holes just to keep things interesting, electronics. No matter how well you shop, bargain, and research in a year, sometimes just a few months, you will be able to get something better for less. Buying anything electronic is an open invitation to buyer's remorse. With electronics it is best to do your research and get the best best you can for the best price. Then make your purchase, and stop looking. Only buy what you need because your ability to resell the item is limited unless you got a really good deal.