I haven't used minnows from my kayak yet but if I do I will use a flow troll that I can drag while fishing then put in the boat while moving from one spot to another. For fish, I use a cooler the has an over flow installed. I fill the cooler up and let the water drop to the over flow and when I need to change the water I fill the cooler back up. Right now with the hot weather I forget about changing the water, I throw a big block of ice in the cooler.
Give a man a fish, feed him for a day.
Teach a man to fish, he'll sit in a boat and drink beer all day.