Im not saying that those things wouldn't help, you think it would be wise just for the ride back home on that saturday? Maybe 3 1/2 to 4hrs or so? 
I wouldn't worry about those for such a short trip. Maybe bring some bags, rubber bands, and water conditioner in case you need to re-bag anything. I personally just try to avoid buying fish that don't look like they are bagged sufficiently - leakers, ones without much air space, cloudy water, significant amount of poop in the bag, etc.
If the auction starts around 10am for example, expect that fish were probably bagged around 2-6 hours before, and they'd probably be fine so long as they were bagged properly and you get them in the tank by midnight as long as they don't get cold.
For keeping them warm, the hand/foot/body warmers that are sold in the hunting departments at Meijer/Walmart/etc usually go on sale at the end of the season (December/January). It's a great way to pick up "heat packs" for cheap! Sure they don't last as ones you might get from a fish supplier that sells 24-36-48 hour heat packs for shipping, they're more than adequate for 4-8 hours usually. I sometimes use them for the drive home from auctions.
