Crisp lettuce is a specific type of lettuce. It is often used for adding crunch to meals.
Crisp lettuce makes the sandwich better.
Add crisp lettuce to your wrap.
This meaning uses 'lettuce' to describe a person as weak or lacking toughness. It's informal.
He is a real lettuce when it comes to sports.
Don't be such a lettuce in this competition.
In this context, 'lettuce' is a slang term referring to money. It plays on the green color of both money and lettuce.
He has a lot of lettuce saved up.
I need some lettuce for my new car.
