Try using a cheap styrofoam ice chest. I have kept minnows alive for over a week at a time in one. The more expensive/ thicker ones don't seem to work as well- no idea why. Keep it out of the sun and if it is going to be hot, poke holes in a bag of ice and drill holes in the lid so the ice melts and drips into the water. Just don't crowd the minnows if you are going to keep them for a while. About 5 or 6 dozen crappie minnows is about all you want in a 26-30 qt ice chest. Remove any dead minnows daily. Also, about a day in direct sunlight kills chlorine in regular tap water so you can add fresh water to your "tank" by just setting milk jugs out to sun. The minnow dealers will hate this but it works.