This, obviously, relied on a certain amount of happenstance over planning; but I got someone the first ladybug of spring once. The longer, colder, winter had been getting her down so, when I ran across a very early emerging ladybug, the first I had seen, I carefully collected it and brought it back as a surprise for her. A small thing; but it worked well with the context.
Another time I got together the materials and equipment so we could make prince rupert’s drops together. In my earlier experiments with them I’d been struck by the strange, delicate, translucent fire of the glass as it came to temperature. I’m not sure how you’d give that to someone; but I wanted to share it with them. As an unexpected extra that glow casts a light that makes candles look harsh and garish by comparison. I can still remember how it swelled in her face and eyes as she focused on the forming droplets, moving from a hint of dull red until suffused with a sort of ethereal rose.
In…slightly…less conventionally romantic tone(and not as a sole gift) I made a π tin: given the recipient’s interest in cooking and epistemology and tolerance for egregious puns it seemed like a good idea. I thought she’d find the tidbit of a case where you can produce a statistical approximation of a mathematical constant by empirical methods to be interesting; so I put together all the bits needed for Buffon’s Needle in a maximally baking-themed package. Parallel lines on parchment paper, procedure written up as a recipe card; all packaged in a pie tin. It went over well; though I suspect that was ultimately more a matter of the fact that she was awesome than the virtue of the idea.
Unfortunately, these instances are pretty ancient history at this point. But I remember them fondly.