Any low-calorie snack recommendations for a late-nighter ? ?

glass of milk ............

Celery, cucumber, bell pepper, etc.

You really need to ask you self why are staying up late and why you think you need food at that time.  Snacking is a reason people gain wait and or have a difficult time losing weight.  Unless you are on  a night shift, your body doesn't need food after dinner.  It is more a psychological desire rather than a nutritional need.  Consider chewing gum and or drinking herb tea with stevia. 

cottage cheese and berries

quark with berries

ricecakes with cream cheese

caseine pudding

fruit in general

vegetables in general