Bonus tip: If you like the idea of having a blue pack, similar to the ones you would buy in grocery stores, add dish soap to the ingredients. This can also be a good way to get creative.
Another good option not covered above calls for using corn syrup. While this ingredient is a good alternative, especially if you want your ice pack to be more flexible, you run the risk of having a really sticky mess if an unfortunate spill occurs. DIY Ice Pack | Todayscreativeblog.net Featured photo credit: Flavio Ensiki via flickr.com