Think of it like a gun. What is a .38 revolver? It's a revolver designed to shoot .38 caliber bullets. What's a Glock 9mm? It's a semiauto designed to shoot 9mm bullets. Likewise, the "weight" printed on a fly rod tells you what size line the rod is designed to cast. A 6wt rod is designed to cast a 6wt line.
The #1 selling rod in the country is a 9' 5wt. It's a very versatile rod and will handle any bluegill fly you care to throw plus trout and light bass flies.
BPS lists 31 combos on their website:
Fly Fishing Rod & Reel Outfits | Bass Pro Shops
I would suggest either the TFO Signature II Series combo or the Redington Crosswater combo. You can't go wrong with either one.