Since we'll be walking long distances in Rome, Florence and Venice....I guess it makes sense to carry a few essentials in a small back pack.
e.g. Mobile charger, power bank, water bottle, pocket diary etc etc.
Do museums / churches / other tourist destinations require you to check packs in at the entrance or can one carry them inside.
Also....are there public water fountains in Florence and Venice , similar to Rome...for refilling drinking water bottles.
Charge your stuff while you sleep in your lodging before you set out for a day of walking; I find there is no need to carry mobile charger, power bank, while sight seeing if you do this. For museums look up each on the web to see what you are allowed to bring in and the lockers
There are some old public fountains here and there but hydrate before you set out and just carry a little water bottle and buy when water needed. More importantly pay heed to keep coins on your pocket to use public toilets (except at museums where the toilets are free).
And carry toilet paper with you.
I found that my devices didn't run down very fast as long as I kept the GPS function turned off when I didn't need it. I think a combination of having the GPS on all the time and taking lots of photos might be a problem.
Sorry to be a downer, but ever since getting caught out during the November 2015 Paris terror attacks, I always carry a phone charger with me. I never want to be stuck in that position again - huddling in a dark restaurant into the wee hours of the morning with the charge on my phone diminishing rapidly while I'm trying both to obtain information about what's going on around me and keep in touch with loved ones. A lipstick charger takes up so little space and weighs nothing (admittedly, it wouldn't keep my phone powered for terribly long, either. For that you'd need a bigger brick. But it would have gotten me through that night.).
So I strongly endorse carrying a charger with you.
I usually only carry my phone with me. It if is warm I carry a water bottle. Otherwise I can buy a water if necessary. Florence does have public water available.
Yes it makes sense to carry a small bag. Key is small! You don't need a ton of stuff, but a few essentials. To me that's camera, phone and charger, small baggie with Advil and tums, and scarf or sweater or sunscreen if the weather calls for it. My guidebook is an ebook on phone or else I'd have that too.
Water fountains - yes, common. Especially in Rome. Many of the historic fountains are still used for drinking water so fill up!
Phone charger - a small power bank is great. Charge it at night and then it can charge your phone during the day as needed. Mine is called the jackery mini but there are a lot of brands. I use my phone as my map (offline maps app) and my husband uses his as his only camera. So battery goes fast. This a non-negotiable essential to me and it's smaller than a pack of cards. Closer to a lipstick in size.
Some museums do make you check all bags and some permit smaller bags. Many allow shoulder bags and not backpacks. Carry a backpack under your arm in these situations or better yet just use a messenger bag. I feel strongly about this (for me, I don't care what others do but I will share my reasons in case they help you). Daypack backpacks are cumbersome. You have to stop every time you need to get something, while with a messenger bag you can access your water or camera while walking. Backpacks are also harder to keep an eye on and present a pickpocket risk. A shoulder bag can easily be carried to your front. Yes, you can put a backpack on your front but then you look silly and like you are protecting something of value. Finally, sometimes I use a backpack luggage - so how would I carry my luggage backpack AND my day backpack in the airport/travel days? Luggage on back, messenger bag over shoulder!
