the finger nail clippers!
For a long time we just had one pair of finger nail clippers, and it was a struggle. I would use them and then subsequently lose them [because I lose everything]. Kyle would use them and leave them laying around. It was a back-and-forth battle over "have you seen the finger nail clippers?" until we finally lost them for good.
The solution? We bought two new pairs of clippers. And to make sure that we don't accidentally use the other person's clippers [heaven forbid!] we engraved them.
And we are officially the nerdiest couple on the planet.