Insulated steel bottle or Nalgene in an OR cozy. My bottle is made by Liquid Solutions-about $20. It will keep hot liquid at least warm all day long in about 10F weather. I made a cozy for it out of a blue pad.

The Nalgene/OR combo works about half as well, but it works.

Or-carry a small canister stove-I do that on day hikes. Mine is a Primus Micron in a Primus pot that I run off a small Snowpeak canister. Everything fits in the pot. Not the lightest solution, but for the temps I am in, works quite well.