LA Burdick's

What to get: Demi hot chocolate (Choose from Dark, Milk or White- they're all delicious!), chocolate mice/penguins, small pastries
Where is it: Harvard Square, Cambridge

Sure, it's not a lot of chocolate for 2$, but each minuscule sip (you'll need to- it's hot!) packs the chocolaty punch of a bar of chocolate. And well it might- Burdick's hot chocolate is essentially liquified chocolate, slightly diluted with milk to keep it liquid. Or at least, that's how it tastes. Either way, it's incredibly rich and more than worth it, despite the size.

(N.B- Burdick's has also started carrying single-origin hot chocolate, which is only available in the small and large sizes. They also have iced hot chocolate, but only in one size at 4.50, though you can usually ask for a demi with ice in it)

(Credit to Robyn Lee via Serious Eats NY)

And if super-chocolaty drinks aren't your thing, or if you have a little extra to splurge, they also offer the cutest mice and penguins made from the same chocolate. Seriously, aren't they just the cutest? They also have macarons (the meringue kind, not the coconut kind) and other little pastries for sale, though most of them are over the 3$ limit.

But no matter what you get, it's bound to be utterly delicious.