I would give them nothing.
Because it's a gift, not a loan or an investment or a stake.
If I lost the 50, the friend wouldn't have expected me to pay them back, so why expect to get what I won?
If the friend expects me to give them a piece of my winnings then they aren't a really a friend and I wouldn't fuck with them no more.
I don't loan out shit, I don't borrow shit. If I give something to someone it is theirs. I don't ask about it, I don't care what they do with it. To do so is to create a debt.