Sounds biased. If food is what gives Luffy strength then Caribou would already be "hax" by your logic. Try harder.
Hancock: Definitely OP. I can only see her going with them EoS, but she already has her own pirate crew. Kuja Pirates, isn't it? She's also very rude and egotistical most of the time (kicking animals that are in her path, expecting compliments and commenting on her own beauty often) and her only bond is with Luffy.
Vivi: I think someone suggested her being a diplomat at one point. Unless she gets a DF or something similar to what Nami has then I don't see her being very helpful in terms of strength. Also, who would take care of Arabasta while she's gone? Koza? Igaram? Pell? Chaka?! Goodness sakes, we don't even know the state that Arabasta is in right now! It's too soon to consider her for
anything until we know what happened to her and if she's even okay.
Bonney: She can age people up, and she's been shown to have great quick thinking skills and can get out of difficult situations by utilizing both her mind and appearance. She has almost no relationship with the Straw Hats though, so probably not a possibility.
Smoker: He's a Logia, so he's already pretty strong. There's just one problem... He's a Marine. I don't get why people even think this is a possibility. No. It's not happening!
Yamato: Journal Writer, perhaps? She could be the one who writes about their adventures. She's also good at fighting and already developed a bond with Luffy. Her Oden obsession is already a turnoff from her character though. The last panel that she was in represented her biggest flaw perfectly.
Carrot: Her fighting style is unique and she's already developed a bond with all of the Straw Hats and not just Luffy. She's a step above Yamato in that regard. She's already shown that she has the skills of a lookout as demonstrated in Whole Cake Island, so the position is already there. I can't say she's shown any leadership skills though...
Caribou: A portable fridge, but with a knife always pointing at your back. A double-edged sword. Talking seriously and logically, he will
never be a Straw Hat or even in the Grand Fleet. No. It's not happening, either!
The position for the 10th crewmember/nakama remains unclear. Only Oda can tell us for sure.