DIY heating pad

This may have already been a thing but idk. Anyways I normally never cramp when I’m on my period but sometimes i do but not often but I started cramping before I got a shower and when I took a shower i figured maybe the hot water would help.. no it didn’t help, so after I took a shower i was like what can i do to make a heating pad because we don’t have one and so I thought ‘hmm maybe a ziplock full of hot water will help’ and it did! I also took some Tylenol to help with the pain but this has help tremendously!!