Oxygen packs, bubbler, ice, change water often.
What works best?
I've been having fairly good luck with an aquarium filter. The self contained type that hangs on the back of the tank. I keep the water level a little below the bottom of the filter outlet so as to get a constant trickling sound with the purpose being to aerate the water. No bubbler, but regularly change out about 25% of the water.
Be sure to scoop out the dead minnows so as not to nasty up the water.
Might get a better response with a duration clause. Minutes, hours, days, weeks, months?
Keep them cool , always use a little net to dip them . Putting your hands in the water kills them .
Engel 13 qt. bait cooler. Have had mine for 2 years. Put up to 100 shiners (usually 60) in it on 95 degree summer days and they last for days. Put water in the cooler from where you are fishing when you get there. Put the bags of shiners in the water. Let the 2 water temps kind of even out then cut bags and let the shiners into the cooler. Dip out dead shiners when you see them. I used shiners yesterday. i caught crappie and no one else had bites. They weren't using shiners. Also caught bass. i generally catch a bunch of bass with shiners. not really trying to catch bass but they love shiners.
i use a 150 quart cooler on the dock with a pump for a yard fountain . then a live well in the boat
I recently read that outing a cup of hydrogen peroxide in the minnow keeps them alive