Funny you mention this.
I went from being a one disc wonder, to a small 15 disc bag, then up to a 25 disc bag, and now Im back to carrying 13 ish discs.
I followed a similar progression.
Started out with 2 discs and a water bottle in a grocery bag (Aviar, Leopard, and 16oz of h2o)
Then bought a used starter bag from a friend for 5$, and carried 4 or 5 discs (Rhyno x2, Roc x2, Leopard)
Progressed through a few bags bigger than a starter, but still small. Mostly for storing food / water / snacks, rather than more discs.
Rocked two different backpacks, always had trouble filling them out with discs though. I like them from a comfort stand point, and how many accessories I can carry....
...but, many rounds I bring my RGD Gecko instead of the backpack. Especially shorter courses I'm familiar with, I'll usually bring a putting Ion, Proxy, Vector, Crave or two, and a Fireball.
There's a cut-off point for me somewhere around the 10 disc mark where I feel like it detracts from my enjoyment. In a tourney, sure, I'll bring back-ups and whatnot. For a casual round where I'm not even keeping score, it seems pointless.
Something I've always found ironic is the more you carry, the more you have to carry. e.g. if I am playing 18 holes with 22 discs in my backpack, I have to carry more water to compensate for the additional sweating I'll do. If I bring my Gecko, I can easily jog between holes to reduce how long I'm out there, and over the course of 45 minutes my body only needs so much water.