i use a small NRS clear dry bag and strap it to the frame next to my seat. i like it because i can see what i need and where it is located for relatively quick access. drybags typicall aren't quick access, but if you need it that quickly, then you're probably not keeping it in a bag, box, cooler, etc., in the first place.
By the waterside I will lay my head.
Listen to the river sing sweet songs to rock my soul.