The biggest thing you can do for your fish to keep them healthy is plenty of fresh water. A good water conditioner such as Prime or Aquasafe, 50% water changes weekly, every week, and you won't have to worry about all the beautifully packaged useless items. Get a quar tank for new purchases, this will keep your main tank disease free.
One thing you can do now is look around the lfs in your area, find the best 2 or 3, and keep their phone number and hours of operation handy. Most fish meds, just like meds for humans, do have an expiration date, so keeping a stock of meds, treatments, and other such things is often a waste of money. If you keep up on maintenance, use a quar tank, and only buy fish from reputable shops or individuals you will have very few problems. The only item you will be using regularly is a good water conditioner.