Disposable
noun, の adjective
After you use it you throw away it, making whatever it is you used a disposable item.
つかいすて
The reading comes from 使う and 捨てる, combined into one.
私にとって、使い捨てカイロは冬には無くてはならないものです。
For me, disposable pocket warmers are indispensable in winter.