I just found the jingle bells.
(I figured you'd all want to know as soon as possible that this Very Important Issue has been resolved.)
They were even in the exact little checkbook box I remembered putting them in (so my mind's not slipping yet, after all). For some reason, they were hidden under/among some packaging supplies-- tissue paper and bubble wrap I was saving to reuse.
(Okay, I know it wasn't the biggest problem facing the world, but not being able to find those bells was really bothering me. I hate not being able to find things when they're needed...)
...Now if I can just get my sewing machine running smoothly again.
I broke a needle on my last project, and after I replaced it, the tension was off (or something). I've adjusted it this way and that... tried a different replacement needle (in case the other was defective)... opened up the bottom to clean and oil it as the manual suggests... took off the side (which the manual doesn't even mention) and oiled a couple of things in there, too. I think the oil may have helped some irritating squeaking it had recently developed. Fingers crossed it magically fixed the other issue, too...