Surprised that some people don't believe it's Kizaru who fed Luffy. The panelling CLEARLY indicates it's him :
1- Sentomaru is arrested and Bonney is in danger
2- Kizaru, laying down on the ground, question his loyalty to the World Government by fearing for his friends : "Sentomaru-kun ! Bonney !"
3- Luffy asks for food so that he can fight Saturn and save Bonney
4- Oda clearly reminds you that NO ONE CAN MOVE, he's not subtle about it so that you can see that even the likes of Sanji are fully unable to do anything.
5- Suddenly, Luffy is eating out of nowhere. Saturn gets mad and asks "who did this ?!" and, who do we see right after that ?...
6- Kizaru ! And on top of that he HAS MOVED in between panels, as he's now sitting against the wall, and is suspiciously having a "..." bubble thought.
It's 100% him. No one can move, and Kizaru has moved in between panels, right when Luffy suddenly got food out of nowhere.
(And he's 100% joining the crew to mirror Kuzan joining the Black Beard's pirates, please Oda)