Oxygen: Goldfish require more oxygen in the water than tropicals do. So an extra air pump or power filter works out quite well for this. Extra air pumps or power filters also have the further advantage that the currents they create in the water help to keep the temperature more even all through the tank.
Feeding: The goldfish is an omnivorous feeder. This means that it eats both vegetable and animal foods. They will also eat at all levels of the water. The mistake made by most people when they first keep fish is that they always over-feed them. Only feed as much food as they can eat in two to three minutes. Remember their stomach is only as big as their eye ball & if you feed more than that it's overfeeding. Food that isn't eaten will fall to the bottom of the tank where it rots & puts harmful wastes into the water. Under normal conditions, a small feeding 1-3 times a day is enough. It is important to feed your fish a variety of foods. Imagine if your favorite food was macaroni & cheese. But you had to eat just that. After a few days of eating nothing but macaroni & cheese it probably wouldn't be your favorite food anymore. Flake food is very popular and easy to get in all pet stores. They also carry a good variety of foods such as tubiflex worms, pellet foods both floating & slow sinking. When on vacation you don't have to worry about having someone come in to feed your goldfish, if they are in good health they will survive quite well for up to 2 weeks. (provided they are in an aquarium and not just a fish bowl)
For more information see my Basic Aquarium Guide . Interested in Tropicals see my Tropical Fish Guide
Links:
Tetra Company Go build your own Virtual aquarium
Sea World Florida, California, Ohio & Texas
Utah Koi and Fancy Golfish Farm Be sure to check out the Fish pictures
Nippon Goldfish Company Go check out the animated aquarium
FINS Tons of fun links