I'm guessing Bleeding Heart bushes may not be totally Valentine's-y. 
Har! Nor 'Love lies bleeding'.

I do like the little bag O candy idea. Anything you might see for sale at a garden centre is up for grabs - wrapping paper, gift bags, sweets - impulse buy things. It's just got to be fairly easy to put together, and then cheap enough to sell on at a reasonable price. I found a web site with herbs that are used in love potions, which is a fun idea. I just can't get too carried away or we will never get it all pulled together in the limited time we have (8 students working for about 5 hours, including ALL the advertising, preparation, set up, pricing, etc)
Passion flower? For non-perishable goods, would it possible to make potpourri?
Great ideas. Don't know if we could make it, but if I got it in bulk and then broke it down into sachets or smaller bags.
Cut flowers aren't viable for the VDay theme (they will never survive 12 days looking fresh), but I guess they could be 'Cheer up, Spring is coming' flowers