A food gather could work but Sanji does all that anyway. He also has been a spy-like character.
So far Nami has been doing alot. She does all the accounting, navigating, makes maps, and she was dressing the crew. She won't stop being the accountant its one of her main passions. She could stop dressing the rest, her taste for fashion is more related to being a girl then any unique to her character.
Who cleans the ship? There is no one that swaps the deck. (if I said that right) So a maid would work and I wouldn't put it past Oda to add one.
A lifeguard character also work, because so far it has been Zoro and Sanji that have to save the DF users. But they are both strong fighters so a lifeguard would allow them free to fight without worry.
The mermaid girl as a tailor/lifeguard could be the next.
With a maid a the next next one.
And I am calling in now, maybe a loli ninja girl DF user to be a spy. And she ate the sticky-sticky DF allowing her to climb up walls and stuff. And she chews gum all the time and likes sweets.