Easier here than on Twitter wher kaputnik and DaveC have queried why I would do this.
I've got a saddlebag for the CX bike already; and last night dug out an old Brooks tool roll I have for the commuter. Yesterday I picked up a couple of items so that both could have everything I could need (within reason) to sort things while out and about.
Kaputnik declared himself old-fashioned and moved bag between bikes. I used to try and do that with the CX saddlebag, but generally failed/forgot/didn't bother for a few reasons. Mainly it was down to the fact that with the Carradice usually on the commuter I don't have space for the saddlebag so don't have a mount for it, but for those rides where I'm just popping out I don't have the Carradice on, so would have to rely on remembering everything I need to transfer to a backpack or the like. Three times I got caught out with punctures where I either didn't have patches or a pump or tyre levers. Always just one thing missing.
Equally, because I commute every day I had the tools in the Carradice, and a weekend ride on the CX bike I'd forget to move something from the Carradice into the Saddlebag.
So for this the Brooks tool roll is great, because it can attach to the saddle and not foul the Carradice.
DaveC raised that he has a light on his saddlebag, and never forgets lights, and so would always remember to move it across. But for weekend rides I'm more likely to be out in the daylight, and so remembering lights doesn't come into my head - they're on the Carradice from the commute, and the Carradice isn't going onto the CX bike etc etc etc.
Anyway, long story short, one bag on each, which just stays there, and which has everything I need.
CX saddlebag has: glueless patches; chain tool; allen key set (with torx key in disc brake size, and spanners); mini pump; spare tube; 8mm allen key (for pedals); tyre levers; cable ties.
Commuter Brooks roll has the above, except the spare tube and mini pump, for which there is no space; and the allen key set does not have the torx key (not needed). It also has a small spanner in addition in the size required for the guards. The mini pump for this bike has been mounted on the frame; and the spare tube... might get stuffed under the saddle.
Just gives me peace of mind that I don't have to think - I can just jump on either bike and hit the road knowing I can cope with most eventualities (have pondered cables for brakes and gears in there as well, but it's probably overkill).
Like I said on the 'swerve' thread - horses for courses. This works for me. Other (higher) faff tolerances are available.