Can you pick them up on your way out? this would be best. Have the LFS bag them, with oxygen if they offer it. Make sure they're double bagged, with the first bag upside down in the second, this way there will be no corners for the fish to get crushed in.
You'll need to carry them in something insulated. A small cooler would work best, or a box with styrofoam, or a styrofoam cooler. Anything that will keep the temperature more stable. The water will cool down over this period no matter what, but the fish can handle it, as long as the change isn't quick.
That's about it really. In bags filled with oxygen fish can last 24-48 hours. If the LFS doesn't have any O2, there is a product available called bag buddies, which is a pill placed in the water to help the fish along, so you can see if they have anything like this.
The ones I got from montreal were bagged and placed in cardboard boxes insulated with styrofoam. The fish were seperated into two large bags.