If the store does not use oxygen to fill the bags with, I had the stores use a larger bag than normal, filled with room air, tied off with a rubberband (no knots!!!) and I brought fish from NJ down to FL by keeping them in a cooler and styro box ( gotten from the store) and I just opened the bags every 3 hours, squeezed out the old air, replaced it with new air and kept on driving. I did this exact same thing with fish when I moved from NJ to FL back in the 70s and again last year. No fatalities either trip. I also asked for a spare bag of water so that I could do a water change should the fish "poo" too much in the bag or in my case, the fish were living in the bag for a week before I drove home so I did water changes even before I left. If the temp in the car is above 70-74 degrees, the cooler temp will actually slow the fish down and make their oxygen needs less and you can stretch out how often you need to open the bags.
There is also the new(?) breather bags which are supposed to be better than a regular bag. I've heard different reviews on them and I have not used them personally but you may want to check into them as well.
If this is an overnighter, you will want to buy or bring an airpump with you along with a gang valve and airstones to use in the opened bags over night. Keep the bubbles low to avoid creating too much oxygen in the water.
On a professional level, as a wholesaler, we packed fish to travel around the globe so with oxygen and a lighter pack ( qty of fish per bag), the fish should be good for 48 hours minimum.
Hope this helps
