Hmm, if I'm only going out for a quick fizz on the road bike, then I don't take anything other than a bottle of water and the pump and bar bag that live on the bike. I don't feel comfy without taking basic tools and spares with me. Plus the bar bag keeps an emergency supply of Haribo and a £20 note, as well as giving me somewhere to put my keys and phone.
For longer rides, I'll generally take the hybrid, which has rack and guards fitted, as well as pump and bar bag as per above. But I have various luggage options; rack bag, one pannier, two panniers or the whole shebang, depending on what I'm doing and where I'm going.
As I rarely have access to motorized backup if things go pear shaped, I do prefer to be primed for all kinds of eventualities.
No idea where my MTB / winter bike project fits into this. It will get its own bar bag and pump, but not yet sure whether fitting a rack is feasible. Maybe one of those expandable saddlebag thing-me-bobs might be a better option...