Depends a little. Usually you are passing through lots of populated places regularly and so generally I would stop at bakeries (local/different ones if I find them) and supermarkets to get the bulk of the food I would eat in the day, as well as the odd restaurant in the evening. I also tour with camping and simple cooking gear so would mix in some cooking depending on time/budget/availability of other options. On my last tour, for various reasons, I ended up doing more wild camping which this time meant cooking less (more evening time spent in towns before finding somewhere to camp) but in say Scotland, would probably be carrying more food and cooking more when wild camping. Always useful to be carrying at least a little food with you just in case you conk-out and need the energy.

An example of a breakfast I was having on my last trip was: 2 croissants, yoghurt with chocolate coated peanuts mixed in, a banana and some fruit smoothie (which seemed on offer a lot this trip) and I might stop for second breakfast/early lunch and get a couple of pasties at the next town with a bakery (handy because you can eat these while cycling). In Italy you might instead be eating things like focaccia from local bakeries (perfect size for my handlebar bag), the landscape of what you eat changes with region, season and mood. You might be surprised though just how good very simple food (bread/cheese) can taste when you are doing exercise all day.

One thing I would advise is that it is a lot kinder on the body to attach the bags to the bike if possible rather than carry on your back. I tour relatively heavy and I think my bike/bags together weigh about 40-45kg, just about liftable at a push if I need to, for example, get a small boat for pedestrians (though usually I'd take a couple bags off to make it easier). It's very possible to travel a lot lighter than this though, particularly if not camping, some people just take a change of clothes and a credit card.

Yeah, just depends on where you're going. We just finished a 4-day tour along the Neckar river in Germany and didn't carry anything extra (except maybe some leftover pastries from breakfast). But then long days up in the north Georgia mountains will require several hearty sandwiches, lots of small snacks, extra electrolytes and maybe a water filter.