By all means steal away! I didn't invent shape packing. lol. Yeah, people tend to be scared of "thieves" but are more than likely also "stealing" some idea or concept from another game themselves. lol. If someone steals my idea I would be excited to see how they implemented it differently / better than me personally! No worries at all! I actually got the idea from dicey dungeons myself. haha
And the packing is mostly as a way to create meaningful strategy consideration when purchasing new coupons / selling coupons. Do you want this super good one? Its gonna take up some awkward space. haha. My game is basically going to be a balatro style rougelike, but since your "deck" is always available (e.g. no 'card drawing') I felt I needed some sort of challenge for players so they can't just load up on good coupons as easily. haha.
Looking forward to seeing what you make!! :D