Welcome Tim.
I use a small, soft sided, insulated cooler that I found at a Dept. Store (Bealls). It's about 10" wide and 12" tall, with a couple of mesh pockets on the sides and enough hooks that it bungees to either my fender rack when I'm solo or stands on the luggage rack when the passenger seat/sissy bar is on. I paid about $10 and its black with reflective piping, so it looks the part. A tool bag on the front forks and I'm all set for day trips.
