My bag can physically carry about 20-22 discs. I sectioned off a small area so I can cram three towels in there so right now I have 10 drivers and 5 mids.
As for the specific discs, I used to carry one of each disc, giving me about seven or eight different drivers and five different mids. The idea was that why force a driver into a line when I can just let the disc do the work. This line of thinking requires you to carry several different molds. I have nothing against this philosophy because if you find the right discs, it is a lot easier on your game to simply throw more naturally and allow the disc to do its thing. This is the same philosophy behind a regular golfer carrying so many clubs. It is likely that some of those clubs are hardly used, but you are glad they are then when you need it the most.
However, recently I have been reducing the amount of molds I have been carrying. I still have the same number of discs in my bag but now I am carrying at least two of each. I am doing more line shaping with fewer discs, meaning I am depending more on me and not the disc. The advantage here is that since you have fewer options to pick from, you have less of a chance second-guessing your self. This is huge because if you second guess yourself, the next time through the course or situation, you may reach for a different disc and the result could be even more deflating; now you have too many choices and dwindling opportunities to find the right disc for that particular shot. The problem with only a few discs lies in that if you are stuck in a bad or unique situation, you now have no choice but to force a disc into something it was not designed to do, adding an unpredictable element to your throw and thus reducing the likelihood that shot is going to be as successful as it could be.
I am not advocating either approach since this debate has been going on since people felt comfortable carrying a bag big enough for so many discs.
Right now I have packed the following discs in my bag: 2 Champion Firebirds, 1 Star Firebird, 2 Firm X-Link Ascents (for testing purposes and have replaced 2 Star TeeBirds), 1 Star Katana, 2 Z Nukes, 2 Star Valkyries, 2 Star Marino Rocs, 2 Star Ontario Rocs, 1 Star Mako, 1 X-Link Ridge, and 1 Firm X-Link Ridge.
In the past when I carried a more varied bag, I also had Destroyers, Bosses, more plastics of Katanas, Strikers, Meteors, Summits, Predators, Tridents, Wraiths, and XCalibers. I basically had one of each and they covered every shot I ever needed to make. As I was sitting in my garage, looking at how many discs I own, because you need to have 2 or 3 back-ups for each disc that is in your bag, I was thinking I own too much for an unemployeed teacher. I chose to slim the bag down in the molds I carry so I do not feel as great of a loss if I get rid of the rest of my discs sitting around.