No biggie, Chloe, just get a few food grade 5 gallon buckets at Home Depot to drain the water into.
-Take the rocks and put them into the buckets and fill with the aquarium water.
-You can also take the clownfish home in one those buckets filled with water. Just reserve a bucket for them without any rocks to prevent them from being crushed during transit.
-I'd remove the sand and get a new bag- a new bag of live sand from Carib Sea or whatever is inexpensive and worth it in this case, in my opinion. It'll make the tank a bit lighter and you don't have to worry about any nasties that may be in that used sand.
-Then when you get home, add the new sand, rocks, fill it with water, wait for it to get back up to temperature and cleared up from the sand debris, and you should be good to add the fish in.
If it's a quick trip, then you shouldn't have to run a heater or air pump. It's a good idea to have a few gallons of fresh saltwater at home ready for this, just in case.