Keep a little zipped bag in my courier bag. Got a multitool, levers, 15 mm spanner, minipump, puncture repair kit, chain tool which is better than the one on the multitool. Sometimes have a cable tie, not currently though.
Always have a fat 700C tube and a thin 700C tube in the bag too (I switch bikes often)
If I was going for a leisure ride I'd just take the multitool, couple tubes, couple levers (ones from multitool went missing ages ago), pump.