Technically you are not allowed to take INR with you when leaving the country, so cash taken abroad is invalid anyway.

Being a annual traveler to India I always take home with me enough rupees to pay for taxis, food and drink to cover for my first day back and I also leave any leftover rupees in a safe deposit box at my accommodation for my next visit, however because I won't be there until mid January I will have to go to a RBI Bank which is not a problem as such but they want proof of where you got the money from? How the hell do I do that?