Army of Peeps
Around Halloween, Peeps website had a code to get 20% off at checkout for any order. It ended up working on all items, including gift cards. So I first bought a $3 gift card, then I used that gift card to by a $4 gift card etc. until I got to an $80 gift card.
I then bought $80 worth of peeps with $3. I told one of my friends and he did the same thing but got his gift card up to $1,600.
Story credit: Reddit / sasha28