hospitals and particularly ers and emts use commercially prepared hot and cold packs where all you have to do is break a bubble of liquid inside the packs to activate the chemicals inside that make the packs become warm or cold. they last for about 20 minutes and then they are thrown away. you can actually buy some of these products in some of the larger drug stores or medical supply stores. you might want to get one or two and demonstrate how they work. just a warning. . .they are expensive. you might visits a few ers, emts or hospitals, identify yourself as a student doing a project and see if you can get some pity and a few freebies of these.
there are also specially designed products that hold hot water or ice. back in the old days there were hot water bottles. it might get a laugh to get your hands on one of these old red rubber things. back in the 50s my mother used to fill a hot water bottle and put it on our tummies if we had a bellyache. these old hot water bottles did double duty as enema and douche bags because they also came with long rubber hoses with the rectal and vagina attachments for these other procedures. there are any number of products that you can find in any drugstore that will hold ice or hot water.
heating pads are also still a home product that are used. in the hospital these are replaced with a electronic product called k-pads or aqua pads which have circulating water that can either be heated or cooled depending on what the situation calls for. the k-pads, or aqua pads, come in various sizes from the heating pad side to a full body size (this is how they get a patient's body temp down, the patient is sandwiched between two full body length aqua pads, a thermometer probe can be inserted rectally to monitor their body temperature and the machine temperature set to keep the water in the pads at a specific temperature). skin precautions must be taken so the patient doesn't suffer a burn or frostbite. you may not be able to get an actual working model of one for your demo (they are very expensive), but you should be able to find a picture of one on the internet that you can print out and pass around or put up on a screen.
for continuous warm moist packs on an iv that had gotten a phlebitis or for someone with a dvt we put a moist towel on the affected area and then an aquapad to keep the moist towel warm on a continuous basis.
for cold packs we got more creative depending on how large an area we had to cover. often we used plain old towels to protect the skin and filled up clean plastic trash bags (because they were larger) with some ice and tied them tightly with knots so water wouldn't spill out as it melted and placed them on the towels against an affected part. the trash bags also gave us a lot of room to sculpt the ice around the body part we were treating. when the water was completely melted we just threw it all out.
something else i would do in preparing this assignment is to go to your local hospital and review the nursing policies and procedures on the applications of heat and cold. talk to the nursing educator and see if he/she has any information that they can give you on this and what kind of equipment the hospital has for the nurses to use when a doctor orders this kind of therapy for a patient. also, hit him/her up for any free samples you can get.