Sanji installs a lock on the fridge within the first week of joining the crew. Otherwise they'd never make any progress on their journey – having to stop for food daily. Two nights after installing the lock though, he's awoken by someone shaking his shoulder. He blinks awake, and nearly shouts (in joy, excitement) when he realizes it's Nami standing over him. She silences him with her hand over his mouth.
"Shh, c'mon." He follows her out of the men's quarters.
"Nami?"
"I'm hungry." She says, unapologetically. She's still dressed, he realizes, ink stains on her finger tips. She must've been working on her maps.
"Of course, what would you like me to make you?"
She seems surprised at that. "I was just going to borrow the key from you."
"But I can make you something just as easily, please." He opens the door to the galley, and her maps are strewn all over the table, giving him just the excuse he needs. "You can keep working while I cook."
She sits quietly, watching him as he unlocks the pantry. "Could you make pancakes?"
"Of course!"
It became somewhat of a tradition after that. She would slip in and wake him, and he would cook her a midnight snack as she worked. He'd then sit beside her, content to watch her work. Occasionally she would nod off, and Sanji would be honored to carry her back to her cabin. Returning to the galley to carefully pack away her maps. Keeping them safe from the fools who would storm into the galley first thing come morning.
If their simultaneous yawning caught the attention and comments of Usopp the next day, well, Sanji was content to let him speculate.