Steal it for life: I recently inventoried my home office supplies and discovered I had about 15 gel pens from my old job. I always kept two in each suit coat or sport coat, two in the car, and 2-4 in my briefcase at all times. Probably a several year supply. I also found a few mechanical pencils and a bunch of lead refills. No telling how long it will take me to use those. At least they won't dry up!
Although not quite "buy it for life," increasingly, I think desktop and, to a lesser extent, laptop computers are becoming "buy it for a very long time" items. Most of our desktop machines at work are about 10 years old and all run Windows XP. They were midrange models when they were new, and I think someone upgraded the memory. They're not incredibly fast, but aren't excruciatingly slow, either. Office 2003 still works fine. Internet Explorer 8 is outdated/insecure and we use Firefox instead, which is still updated on XP, as is Chrome. These are all midsize towers--one advantage of the tower form factor is that they usually use a standard power supply and other parts instead of the proprietary ones in the small form factor machines, hence, they are easier to repair.
With laptops, you have the whole battery issue to contend with, but those are much improved in the past few years. The one in my 3.5 year old notebook will still hold 87% of its rated capacity after over 500 charge cycles. I think it's reasonable to expect at least a couple more years out of it.
Tablets and cell phones, on the other hand, tend to be anti-"buy it for life" purchases. I resisted upgrading my iPad mini from iOS 6 to iOS8, but newer versions of Chrome and some other apps required a newer operating system. Apple seems to offer iOS upgrades for about three years from the release date of a device, and it's a given that a device will get slower as the OS becomes more complex. Eventually, new apps will not be released for the older operating systems, websites will cease to function properly on older browsers, and the device will become obsolete. The situation is likely worse for the Kindle, as you are generally stuck with whatever version of Fire OS the device shipped with. Google used to follow the Amazon model with Android but is getting better. I think the lifecycle is much shorter for mobile devices than it is for traditional desktops/laptops.