peg,
it will depend on some things.
i try to keep my hands free. I will probably have a camera in one and if im thirsty i may carry a disposable water bottle in the other until its gone. I try to use public water fountains when possible, keeps the carrying to a minimum.
i have Point N Shoot cameras so i can put them in my pockets when not in use.
as far as maps, i usually have a paper one so that isnt an issue.
as far as buying souvenirs, i do that but i know what i will buy so that i either buy it on my way out so i dont have to lug it around or i have my "buying" day(s) or will buy it when im going back to the lodging. Either way, im not carrying stuff all day, but at the most half of it.
happy trails.