First, read over these pages on my site:
http://www.fishpondinfo.com/gfish.htmhttp://www.fishpondinfo.com/snail.htm and the apple snail section on
http://www.fishpondinfo.com/snail2.htmGoldfish absolutely should not be kept in bowls because they are large, fast growing fish. I've had many 12-14" long. The "golden snail" is probably an apple snail which also grow large. Mine's almost tennis ball sized. See applesnail.net for more on them than you ever wanted to know. My biggest recommendation would have to be to get as large a tank as you can, ASAP. In the mean time, at least try to put in an air stone for aeration.
Snails don't need a reason to float around. They sometimes just do it. He may be stressed. Have you checked out your water quality? I mean testing the pH, ammonia, nitrite, oxygen, and chlorine levels? Did you use dechlorinator? You REALLY need a larger tank with filtration and aeration. A big reason snails will hang around the surface is to get oxygen. They can breathe air somewhat. Since you have no aeration or other water movement, the oxygen levels are probably low. The goldfish may also gasp at the surface if it gets too low.
The snail can live on just fish food. They do love veggies so you can try those. The thing is that in a small bowl, those things may increase the pollution such that the negativity of that outweighs the benefits. The goldfish will also try to eat the veggies and make a mess. In a tank with filtration, that may be ok but a bowl may quickly become fouled.
I really pains me that pet stores and most people think that tiny fish bowls are adequate homes for any animals, let alone goldfish. So many animals have died as a result, and many children have lost their buddies. I suggest you buy a 20 gallon tank to start. If it's too expensive for your budget, try getting a used one. Good luck!