As indicated by a recent thread, its really not a good idea to stuff your handbag to the gills(as we all often do!). Not to mention that lot of handbags are very heavy even empty-take Florentina Vachetta from D & B-gorgeous bag, so stylish and so darn heavy, that even empty feels like its loaded with bricks.
Personally, I recently had to reevalute what I carry in my bags as well as start getting lighter handbags because I was having back pains and extra handbag weight wasn't helping. So what do have in my bags now?
wallet(which is actually a leather skinny from Coach)
phone
small makeup bag(only eyedrops, compact, lipstick and nail file in it)
small notebook that I use for notes and app(yes I can mark app on my phone but I prefer writing it down in the notebook, its about 2x4 size)
Kindle(I have kindle touch which is extremely light and weighs next to nothing)
Umbrella(a necessity where I live since it rains at the drop of a hat)
And during the week I also carry my lunch and bottle of wated. I guess this is my minimum.
As far as the lightest bag I have encountered, its without a doubt Longchamps Le Pliage, as its made of nylon with leather handles. I use mine all the time. I just got leather Coach satchel that is also very light