Last year one of our smoke / CO detectors died. I searched for a replacement and the kind we used was discontinued and on sale. We have 8 interconnected detectors and I was concerned that in the future if another detector dies will the new one still work with the other 7. Since they were on sale purchased what they had. If I recall, I have 5 for the future.
Just a few days ago one of our LED recessed ceiling lights (can light) died in the kitchen. It was maybe 6 years old. So much for LED bulbs lasting 20 years. We went to Menards and I found the recessed light I needed but.... the manufacture changed the appearance. We use 21 of these lights. The kitchen has 5 of these lights and the family room has 9, Of course the all match. I purchsed 24 of them (all they had). I'll install the new light in a bathroom, and move the bathroom light to the kitchen. The lights in the kitchen match again. I hope I have more than enough lights for the next several years, or more.