Honestly? The cheap stuff. What you're making is basically an antifreeze solution, as alcohol has a lower freezing point than water. The first one we tried was 2:1 water to alcohol, according to the online directions, and it still froze solid, so we went with 1:1 ratio and filled a quart zip bag only half full, squished the air out, then put that bag into another(the zip side going to the bottom of the new bag. That way, it's unlikely to spring a disastrous leak.
Mine last several weeks with heavy daily use, but I can also drop and break unbreakable objects; it's an anti-knack.
Ice?
If you have access to a bottle of plain old rubbing alcohol, 1 part rubbing alcohol to 1 part water makes a good, slushy ice pack instead of a brick.
Re: Ice?
Re: Ice?
Re: Ice?
Mine last several weeks with heavy daily use, but I can also drop and break unbreakable objects; it's an anti-knack.