Roll up cold beer or hot bottled coffee in your sleeping pad and cap both ends with some spare clothing. I have had pretty good results doing this. Of course all bets are off if your sleeping pad serves as the framesheet for your pack.

That works great. I also use my down jacket as my camp kitchen "cozy"... works way better than the cozy I made and tried using for awhile, much higher R value.

I often use my clothing or sleeping bag as a cozy, but always wrap the hot/cold item in a plastic grocery bag to prevent condensation or leak issues.

B&J's wrapped in Western Mountaineering Ultralite FTW.