It's been awhile, but last I checked, buying "packs" was less cost-efficient than buying individual ferts, and you're unable to customize.
As Hoppy says, you want a 4:1:1 ratio of a nitrate (KNO3), a phosphate (KH2PO4), and a micro/trace (CSM+B). In addition, you want a potassium source (K2SO4 or GH Booster), though potassium is also provided by the first two ferts. If you've got a low GH, get GH booster. If not, maybe a bit of K2SO4. GH booster also includes magnesium, manganese, and calcium.
Some people recommend iron, some don't. Some claim it brings out the red in plants, some claim it doesn't. If you want to give it a shot, try using it at 1/2 the dose of CSM+B. Good luck!