I think I am the only one who mentioned opening rear pannier, so this is probably for me to answer.

It's not necessarily rear pannier or any specific bag that I think is especially important, it's just that I personally pack that way.
When I am on a tour, the rear left pannier holds everything I might want during the day that does not belong in handlebar bag and is not food related - spare clothes, rain jacket, toiletry/hygiene bag and towel, sunscreen and insect repellent, swimming trunks, slippers, powerbank and its charger... At the very bottom are dirty clothes, which are also taken out during the day, when or if I get to a place where it's convenient to wash them.

So, the handlebar bag and rear left pannier I open multiple times every day. Every other pannier or bag holds very specific things and are opened only when, or if, their time is up (sleep time, food time, fix puncture time, oh God no a technical problem time, oh crap a long tunnel time).