Cheap way to keep water hot?

[la79al]

We are going Christmas caroling tomorrow night and I am in charge of supplying hot chocolate. Problem is that I don't own a thermos and in order to get one that will be big enough for our group, I would end up spending at least $40. I did get a 1 gallon water cooler thing that specifically says not to use with hot liquids but I was thinking maybe it would be okay for a single use. There is probably a really easy solution to this but Christmas and a sick baby have fried my brain.

 

[tchrrx]

Do you know anyone in the neighborhood where you'll be caroling? Does your church or school have one of the big pots that are used for hot liquids? Maybe someone in the caroling neighborhood would be willing to keep the water plugged in and hot, and then you all could fill cups with instant hot cocoa upon arrival.