Never buy expensive:
golf balls: I’m an inveterate ballhawk, so I play what I find. Anyway, all new balls are so similar and so well made, you are a fool to buy the current hype and think it will improve your game.
coffee: I’m a coffee slob. For me it is all about volume and strength, not taste.
aspirin: if it is chemically aspirin, the name doesn’t matter.
hobby supplies - for me fish, plants, and aquarium supplies: this one might be a little obscure, but it may have analogues for some of you. I keep several planted aquaria which I treat with various fertilizers. You can buy these little bottles of diluted liquid at fish stores, which would probably cost me @ $10 a month to treat my tanks. Instead, I was able to mail order the chemicals and bought a several year supply for $25 (including shipping). There are substrates I can buy locally for 1/10 the price of commercial products. I trade weeds with folks on-line for no cost other than mailing. And a local fish club has periodic swap meets where I can get just really healthy fish for a fraction of the price at fish stores.
Never buy cheap:
chocolate: My wife, the chocoholic, has quite discriminating taste in this area.
ice cream: Anything lower than Edy’s isn’t worth the calories.
furniture: once you have had nice furniture, you not satisfied with the cheap stuff again. With uphostered, you will be feeling the frame on the Crate and Barrell stuff within the year. Unuphostered, get something you really like and you will be able to hand it down to your kids.
butter/shortening: cheaper just doesn’t bake or taste right.
paint: nice paint applies and wears much better than what is on sale at Sears.