Kajero, I have a Topeak seat bag. I have had several of their products, in varying sizes, on different bikes. But, the Cannondale one I had before held a lot more and still fit on my teeny bike.
Even I can use the CO2 inflator. The one I have has a button you push and it lets you release various amounts of "gas." There are also various types of cartridges and I think some are better than others (threaded vs. unthreaded). I carry 2-3 cartridges and 2 tubes.
I have never worried or obsessed about my phone or wallet... am I weird? I stick my credit card sized regular wallet and my phone in my jersey pocket and go. When I first started riding, I put them in my seat bag, but I stopped doing this when I wanted more room in my bag.