I'm going to end the pay-it-forward chain at the fast food drive thru and then spend my savings/unspent lunch money at goodwill
Why are you making that decision?
I can't afford things most of the time, my money is going to goodwill, I don't need a gift from strangers I can get it from my grandma.
It is a nice gesture to pay it forward.  However, the bottom line is it is okay to spend your money the way you want to.
I don't think it's nice so I'm not willing to be a part of it.
ok it's cool even if you don't be a part of pay-it-forward chain. It's your money and you have all the rights to use it the way you want.