Also network cables. After spending days troubleshooting weird network issues a few too many times, I just toss the entire box of miscellaneous network cables in the attic every year or two.
But capacitors are definitely the second most common issue.
Way back when I was a staff engineer at Motorola, we'd often have network problems from workstations caused by marginal cables. At first, the IT people would come over and replace the cable, and toss the bad/old one in the person's cubicle trash can.
But I noticed over time, they all started adding one extra step: they'd cut the cable in half before tossing it in the trash.
Before the cable cutting, engineers, being engineers, would fish the "bad" cable out of the trash as soon as the IT person left ("it works almost all the time...") and use it for the next lab build-out. And then integration tests would fail intermittently, etc.
But capacitors are definitely the second most common issue.