I have a saddle bag on my bike at all times with tyre levers, puncture repair kit, mini-pump, asthma inhaler and my phone, it can expand to fit more as well but not needed that as yet, could do soon though.
I did buy a top-bar bag (Topeak Tri-Bag iirc) and can see how it'd be good, found it kinda irritating when I stood up to pedal but then I try not to do that much (but junctions and steep hills I 'need' to for short periods).
And then for work I always have a rucksack with whatever else I need...
On a related but separate note, is anyone doing the Wiggle New Forest sportive this weekend (Saturday specifically?) I signed up a while ago as my first sportive, then recently upped the distance from 44 miles to 65 as I felt, even though I've not ridden many long distances, that 44 miles would be 'too easy', think I was a little crazy at the time
Looking forward to it but also a bit nervous, also not 100% sure what to take so far, don't really want to take the rucksack along with me to store stuff in as it gets dryer/warmer (assuming the predictions are right) during the course of the ride. I have got myself a spare innertube (well 2, only gonna take 1), replaced my mis-matched water bottles with a pair of 800ml ones which will be way more than enough between the food/drink stops, not got a multi-tool to take other than a leatherman which I'll chuck in but isn't really bike specific. Anything else I'm likely to forget?