I currently use all of the above!
I have an Ortleib Saddle bag, which is really robust and rolls shut like a drybag. The mounting bracket can also be bought separately, so I have one on my Bamboo bike as well. It's just a matter of minutes then to put the bag on which ever bike I'm using. It's a really nice saddle bag which can fit a surprising amount in.
In the frame I have a 6 litre Topeak frame bag, which I use for a spare fleece, food or waterproofs. On top of the frame I have a 1½ litre fuel tank, in which I place keys, wallet etc. It's quite tiny, so not a lot will go in there. One problem I have, is because I have a steel framed bike, the tubes are round and so the fuel tank is always slipping off to one side or another as I ride. The flatter profile of top tubes more commonly found on Aluminium and Carbon bikes, would stop this.
Because of the frame bag, I have to use 500ml water bottles in the frame and one cage has been relocated further down the frame using the topeak alt-position bottle mounts. I'm lucky to have bottle mounts on the fork legs, so in the summer, I'll carry an extra litre sized bottle on a fork leg. Under the down tube, I also have a bottle cage mount under the downtube in which I store a tool caddy for all of my tools, this stays on the bike permanently and frees up room in my bags.
To be honest it's all a little overkill and most of the time the bags are half empty, but they weigh very little and it's no hassle to have it all on there.
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