Even if you don't know them well, you probably know more about them than you realize. Repeating some ideas from others, but:
Do they drink coffee or tea or hot chocolate at work? Maybe a mug with a coffee gift card, or a box of tea or packets of hot chocolate.
What kind of snacks at work interest them? Do you bake or make candy? You could give them homemade bread or cookies or candies. Or if they don't eat many sweets, you could make up a small fruit basket.
Water bottle or tumbler with straw to use at work?
If your workplace is chilly, fingerless mitts/hand warmers?
Do they have pets? Something pet-related like a fun dog book or calendar. (Shake Puppies is about $10 on
Amazon, though you don't have time to order it--but something like that?)
I'd avoid scented candles and lotions unless you know for sure they don't have issues with them -- I'm very sensitive to scents, and so are a number of my coworkers.