Wool
It's become an extended-family project for the Uhura clan, collecting wool.
They don't really know why they are doing it – Sort of, but not really. It's just something that started when Nyota was at the Academy (no one quite remembers how, or when) and they've been doing it ever since.
(And he doesn't know they are doing it; but, still, he is one very smart man…)
Nyota knits; and as she does, she feels the love of her family in every millimeter of yarn that passes through her fingers and over her needles.
They travel a lot, her family; and as they do, they haunt the yarn shops, buying sock-weight wool in charcoal grey or black. Sha'mi is best: The fine Vulcan wool, with its distinctive aroma, comes naturally in those colors (and in a lovely rich dark chocolate brown, too). If that is available, they will buy it. Though scarce, it's not truly rare yet - but they figure 'some day soon' - and they buy all there is, even if it's only a blend.
And in sweater weight, also, because they love Nyota, and she knits sweaters, too. (Uhura Clan logic is a logic of the heart.)
But if there's no sha'mi, they do the best they can: They buy sheep's wool and merino and alpaca, and sometimes blends with silk.
(And sometimes they throw in something frivolous, something bright and just for fun, remembering fondly - without regret - the time when that was what Nyota liked…)
The packages she receives are bulky and light, but overflowing with love and hope, and concern for her health and happiness.
And those wools will keep her busy on the long nights when he is away.
She will be busy on the nights he works late.
Her hands will be occupied as she sits by his bedside in Sickbay - and sometimes as they just sit together and talk, in the little time they have alone.
She knits him socks, from the wool they send, and she's made so many that it's a science, now: She can look at a yarn and know how many stitches to cast on - on which size needles - to make him socks that will hug his ankles, wrap his insteps, keep his toes nice and warm – to feel wonderful, like a lingering caress, between bare Vulcan skin and boots.
She knits him socks, and every stitch is formed from the constant love she has for him.
As she knits, her heart and mind whisper all of the words she cannot say as they work side-by-side, as they walk in the corridors, as they go about their days in the public eye.
She knits – as though love and silent whispers and hand-knit socks can bring him home in safety.