When I have a cold (as I do now) I find that applying heat to the back of my neck seems to bring some relief from congestion, and the easiest way to do this is to fill a sock with uncooked dry rice, tie a knot in it, heat it in the microwave for a minute and hold it in place with a hoodie.*
You can reheat the rice sock multiple times, and the smell is quite comforting. It can also be good for cramps and is a lot less bulky than a hot water bottle.
* obviously make sure the temperature isn’t too hot before placing it against your bare skin