Gum Drops

Gum drops are a food item found in Fallout 3 and Fallout: New Vegas, and are used as an ingredient for mushroom cloud.

Characteristics
Gum drops restore some of your Hit Points and cause no Radiation poisoning, but they are very rare in Fallout 3. While the box says "Radioactive", the gumdrops have a lower radiation count than other food items (1, as opposed to 3). Because of this, even a slight radiation resistance can negate this, rendering it in-game as 0. Gum drops are one of the rarest consumables in the game.

Fallout 3

 * At A Quick Fix in Rivet City. It must be stolen from the shop and does not appear to be for sale in the owner's inventory.
 * In the Jury Street Metro Station area, south of the station inside the drainage chamber (see Dead Man's signal).
 * James Hargrave and C.J. Young carry them, they can be pickpocketed. Only with high Luck, they may also carry bubblegum.
 * In the Vault Theme for your Megaton house; one appears on the shelf with the food on it.
 * During Broken Steel, three can be found in the Mobile Base Crawler. One in the base floor behind a Repulsion Field along with other items, and one in the launch platform base, in the toilet cubicle which hasn't been flushed (and that an Enclave soldier has apparently been having some nasty problems involving the removal of his intestines after ingesting these). The third can be found at the southeast corner on the ground floor behind a Repulsion Field along with chems and other first aid supplies.
 * During Broken Steel one can be found in one of the Eat'o'tronic 3000s in Old Olney Underground.
 * In Point Lookout, the panic room under Calvert Mansion has two boxes on a shelf, along with a Nuka-Cola Quantum. The hatch to the panic room is visible only when the mansion is destroyed.
 * In Point Lookout, in the People's Bank of Point Lookout, in a safety deposit box.
 * In Mothership Zeta, in the Cryo Lab (which can only be accessed prior to finishing the main quests).

Fallout: New Vegas

 * Inside the Great Khan hideout in Boulder City ruins, on a shelf.
 * Several packets can be found in the Nipton general store.
 * Gum drops can be bought from various merchants.
 * In the Dead Money add-on, five packets can be found in the gift shop at the northernmost tip of Puesta del Sol.
 * Three packs can be found inside Vault 19 in a bedroom in the living quarters, on a shelf. The shelf is over a bed.
 * During Honest Hearts, gum drops can be found in the General Store on the display case directly in front of a silenced .22 pistol
 * Two can be found in the El Dorado Gas & Service, one in the display, and the other on a shelf near the door. (Sometimes one will be on the floor, instead of on the shelf.)
 * One pack can be found on the top shelf in the Camp Golf kitchen, but it is considered stealing to take it.