The cupcake thing is hilarious, that gave me a good laugh!
What I'd do with the cake box moocher is tell her sure, she can buy boards from you, here's the price list. Then double the price that you paid for the boards, since you're now acting as her wholesaler, and that's what wholesalers do. Make sure to take your shipping costs into account and add those in too! And if she wants you to lug the boxes in to work then that will be an extra delivery charge. Just hand her a price list and tell her that's what it will be,and if she'd like to place an order you'll need at least a couple of weeks advance notice ini case you have to order more from your supplier.
i've sold boards and boxes to people in my area, but they were polite about it so I didn't give them the wholesale treatment. Rude people get the special surcharge.