A Spoonful of Whiskey

 is a Fallout 3 quest that is added to the game with the Point Lookout add-on.

Walkthrough
Marguerite will try and convince you that she is sick, and she needs these items to get better. With Medicine and Speech she will admit she makes Moonshine and ask you to gather these items for caps as well as a share of the Moonshine.

You need
 * 3 Yeast
 * 6 Fission Batteries
 * Either 10 Refined Punga or 20 Wild Punga Fruit

It is a wise idea to travel light and find a way to get the fission batteries and punga fruit to Marguerite. The required items will total a massive 70 lbs., or 80 if you're carrying wild punga; if you're also carrying the required 12 pounds of Yeast, that's 82 or even 92 pounds on top of your other equipment.

It is possible to bring the items per batch to Marguerite; this may be a more weight-efficient way of completing this quest. You can also drop the items in her kitchen and retrieve them later once you have them all.

A good place to find both the Yeast and the Fission Batteries is Blackhall Manor. (if you haven't already taken the items.) The Yeast is all around upstairs and down and the Fission Batteries are upstairs look everywhere there are 6. There are also another six in the panic room if the house has been destroyed. You can get the Refined Punga Fruit from The Ark & Dove Cathedral after you have completed the Walking with Spirits quest.

Reward
You will receive 300 caps and several Moonshine. You can also repair her still for an additional 100 caps (200 with a speech check).

Trivia
The title of this quest is probably a reference to the song "Just a Spoonful of Sugar" from Mary Poppins.