What do college kids love more than anything? Sweet sugary treats. And most college campuses are remote from choices. And college students are LAZY. Show up at the dorm with Girl Scout Cookies, you'll be flooded with sales!
Nostalgia sells. But, as Julie Tilsner notes, you'll want to suit up first in full Girl Scout regalia. Maybe the woman across the hall from Grandma used to be a troop leader and can wax nostalgic about the old times.
No point swimming against the tide. If people are already in a food-buying mood, what better time to get them? Best of all, they can get cash back while they're shopping and you won't have to mess around with spending limits.