The heat pad only works once.You can heat up the quickfix multiple times but the heat pad is a chemical formula that you mix up in the bag and once its been used thats it.
3 options: Have a microwave close that you will have access to, to heat the quickfix or get system down where you can leave the bottle of quickfix stashed next to your skin where it will always be warm.
You could also buy one of those pocket hand warmers and stuff it and the bottle in a sock and keep it in a pocket.