Dogtrousers
Lefty tighty. Get it righty.
The tools i need to keep me on the road take up very little room. My allen keys, tyre levers, chain tool and puncture patches fit in a neoprene case intended for a compact digital camera. I keep it in a small saddle bag but it will wedge under my saddle or sit nicely in a pocket. Would the OP see my tools if i didn't have the saddle bag? I very much doubt it.
Another option is a tool bottle. A friend if mine uses one. You can fit quite an extensive kit in there and it wouldn't be obvious to a casual observer that you were carrying anything.
Obviously not ideal for long rides in hot conditions with no access to shops as it restricts you to one bottle.