Chocolate, always chocolate, and make it good chocolate. For example:
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You can do themed care packages--say she's a tealover. Do a care package with a variety of teas, tea accessories (tea infuser, teaspoon, mug, whatever), and a box of shortbread. Coffee? Variety of coffees and a mug. Puzzles? A whole boatload of different kinds of puzzles. Maybe she's into knitting? Yarns, a knitting book, and a size of needles she doesn't have.
Ultimately, the care package isn't about us, but who you are sending it to. And if you don't feel like spending too much $, baked goods are generally appreciated.