That's one of my big questions, too: Where was she all day? And why did she need all that cash?
I like your idea about cash and carry, but with Jeff's recent follow up interview, he says that she didn't currently smoke. Which leads me to wonder, again, if the money was meant for a bribe/kickback from someone (or to someone). If she was the mole, then perhaps the money was given to her as incentive. After all, in Jeff's initial interview, he did say that she needed money lately.
Or, conversely, it could be that she needed money because someone else was extorting her for some reason. Which I suppose is a reason both for her being the mole (to get kickbacks) and also to pass along money to someone else (cigarette box) who was shaking her down for cash. Maybe someone found out about her being the mole and wanted in on the deal.
Bleh.
Then there is the whole situation with one of the Grubmans sneaking off late at night with the headlights off. That seems awfully suspicious.
And, Meg's telling her boyfriend that she needed to get some work done, and then claiming to have gone home, moonbathed, and drank wine instead.
Ok, I'm done conjecturing. We need more information!