For me it was a custom little "shield" for my garage door sensor - it was originally installed on the wrong side so the sun blinds it for a few hours a day a few months out of the year. Instead of standing and holding my hand up to block the sun or moving it and re-aligning it - I just made a little cap brim that shields it.
Ha, my sister had the same issue. I tried creating a tube, but at sunset at a certain time of the year there was no stopping it. Unfortunately, the wires were run behind the drywall, so I had to cut the wires, and swap the emitter and receivers. Curious how your shield was designed, though.
As for my most useful print(s). First, I bought my daughter an inflatable gymnastics mat, and it arrived a few days before Christmas, only for me to realize it uses a special pump to inflate (I learned it is a Halkey-Roberts valve typically used in stand up paddle boards). No place that sold pumps could get it to me in time, and I really wanted to have it inflated for Christmas morning, so I found a Halkey-Robers valve adapter on Thingiverse, and then found a replacement valve adapter for the Coleman air pump I had, did some slicing and mashing together in MeshMixer, and got to printing. The first one didn't work, but after a bit of adjustment, the second print worked and I was able to inflate her mat so she could use it.
On the vintage Mac side, I'd say my most useful ones were the feet for my Quadra 700, the BlueSCSI mounts for my SE and SE/30, and my external BlueSCSI cases.