You should tell the LFS how long a drive you have, so that the staff can bag the fish appropriately. I agree that under normal conditions you should be fine, but if you're buying more than 1 fish, it might affect bagging.
All the decent stores are easily an hour away from me, and I usually hit more than one store in a trip, and stop for dinner on the way home, so it's not uncommon for the fish to be bagged for 3-5 hours. Hasn't ever been an issue. I do give the stores a heads up that they'll be in transit for a while so they'll pay a little more attention to how they're bagged.
It's as much how they are bags and how the bag is treated more than the time. A large group of fish in a small bag with little air at the top can be killed very quick if careless. Left in the sun on a hot day?
Give the store a headsup that you are worried or do just a bit more to protect the bag. Taking a small styro cooler will make the trip much better even if there is a question on the bagging. Gives them a better chance if they are in the dark rather than all the bright lights and scary things.
+1 with PlantedRich. How they are bagged is a huge part in it. After going to a number of auctions including the ACA, I've noticed there are people with perfectly fine and healthy fish but they die after 6-8 hours in the bag because they aren't bagged properly. Think about the ride the fish take when they are shipped from Europe, Asia, Africa and South America. If bagged properly, they can make those trips so a little trip from the fish store should be nothing.
If I remember correctly, when bagging fish for a long time (I just moved and bagged up my fish) its 2/3 air to 1/3 water. This is the way I bagged and my fish were in their bags 26 hours I think? You want lots of air, and then little water. It prevents them from banging into each other and jumping. I bagged all my fish individually and then popped them in a Styrofoam cooler. I didn't lose a single one, if you are traveling 6 hours or less I suggest a backpack lined with towels or blankets, Then wrap them up and in the backpack. Make sure to keep the bag with you and covered. I know its hard not to peek but it stresses them out. I did this with shrimp, CPDS, it really helps them. Also you want to prevent a lot of temperature changes thats why they towels.
I knew someone that made they own fish bag covers out of felt and wrapped every fish bag from the store in them and then straight home. I think they lived VERY far away from fish stores.