Luffy -> Panties (Brook)
These are from the backpack that Hancock gave him from way back in Sabaody. Luffy literally forgot about them and randomly found it one day so he just gave them to Brook.

Zoro -> Cash (Nami)
Didn't know what to buy so he just gave her cash.

Nami -> Mini-Going Merry (Usopp)
Knows Usopp loved Going Merry so she commissioned Franky to make a small version of it as a gift.

Usopp -> Shark Costume (Jinbe)
He thought it would be funny since Jinbe is a shark. He made the costume himself! Truly a man with many talents.

Sanji -> Meat (Luffy)
This is an attempt to keep Luffy from raiding the fridge during Christmas. ^{It didn't work.}

Chopper -> Fridge (Franky)
Chopper actually put thought into the gift because he's a good boy.

Robin -> Cotton Candy (Chopper)
Knows Chopper loves it so it was a no-brainer.

Franky -> Porn Magazine (Sanji)
A perverted gift from one pervert to another. To no one's surprise Sanji appreciated it.

Brook -> Skull (Robin)
As a skull joke Brook literally gifts a skull.

Jinbe -> Booze (Zoro)
As a newcomer he went with what he felt like the safest option. It was some very high quality booze.