Flour (Fallout 3)

 can be used as Rock-It Launcher ammunition. However, its more important use is as an ingredient in Mississippi Quantum Pie. It is not listed as a food item, but rather as a junk item.

There are only two guaranteed samples of flour to be found out in the world. one of them is located in a diner roughly north of the Nuka-Cola Plant and west of the Red Racer Factory. The other is located in one of the mailboxes at the small town next to the Corvega Factory. Several vendors are known to sell flour:
 * Gary Staley and Seagrave Holmes in Rivet City
 * Lydia Montenegro in Tenpenny Tower
 * Moira Brown in Megaton
 * Knick Knack in Little Lamplight
 * Michael Masters in Warrington Station/Tenpenny Tower
 * Karl in Meresti Metro Station
 * Crazy Wolfgang (after you invest in his caravan)

There is a small chance Flour will be available for sale by other vendors and scavengers, so check their inventory on other days if it is not available.

Flour can also be found in the kind of random loot typically found in schools and kitchens.