It depends on how long the trip will be and what temp you are expecting to go thru durnig the trip.
As a general rule, you should bag each fish individually. For a guppie, you could put them in around 2 cups of water each. Pack all the bags in a styrofoam container. Make sure to fill any gap beetween the bags with paper or more plastic to avoid the bags from rollin from one side to the other. Close the lid of the styrofaom and you are ready.
If your trip is long, you could think of adding bag buddies. It's a product that sedates fish and reduces stress.
Another tip: don't feed the fish 2 days before the travel. So you'll have less wastes in the bags = less ammonia buildup.
Almost forgot: the styrofoam container should keep the water temp stable for sometime. when closing it, make sure it's tightly sealed.