F.U.N.C. Barrels are map items that spawn randomly around the map. They are very similar to former contestants, except they are rare, take longer to use, and reward you with 15 F.U.N.C., while former contestants are very common, are used very quickly, but only give you 5 F.U.N.C.. Also unlike former contestants, F.U.N.C. barrels have predetermined spawn locations (similar to item crates and explosive barrels), and each location has a chance to spawn each game.
Beware though, whether they are empty or not, F.U.N.C. barrels are highly explosive and will detonate after receiving 10 damage. This will deal 25 damage and bleed * and cripple * to any player standing near it.