A fish that small could be moved in a well cleaned jar or a freezer sized bag. The only thing to be concerned about is that the is enough air in the bag. Without the air, the water will quickly become short of oxygen. In our club auctions, the instructions for sellers suggest 2/3 air and 1/3 water in the container. A molly should be fine for temperatures as long as it doesn't drop below 70F, 22C.