I switch bags fairly frequently though not quite daily. I used to use one of those purse inserts and it was nice. But then I went on this long jag carrying nothing but clutches (with wrist strap) - easier on the back - and the insert wouldn't fit into it. (For work I'd just toss the clutch into my laptop bag, which has wheels ... yeah... not fashionable but boy does it save my back.)
The clutch jag taught me to be a minimalist, and I was already a minimalist when it came to what I carry in a purse. Here's my strategy:
1) I stock all my purses with certain common supplies such as hygiene products, Kleenex, gum, and a couple of band-aids. No transferring necessary; it's already in the bag.
2) I keep car keys and sunglasses in a bowl near the entryway -- basically any item you might grab without your purse to go outside (for a walk, walk the dog if you have one, quick run to the car, etc). This way, these items are dissociated from your purse. You make a habit of adding them to whatever purse you happen to have settled on.
3) I transfer from purse to purse only these items: a) foldable comb/brush b) lipstick c) wallet (which happens to be a clever wristlet design that also fits my iphone).
Actually, with lipstick, I often have older tubes in each purse. So if I forget to transfer my current in rotation favorite, I'm set because there's probably an older one rattling around. I also have a chapstick attached to my keychain. So I am never ever without some sort of lippie. I do not bother packing any other make up in my purse.
What's nice about this strategy is I only have to remember and transfer just three items. (well I also have to remember to take my iphone off the charger and put it into the wristlet, but I'm so enamored of my iphone I never forget to do that!)
4) Last thing I do is stash a cardigan and/or a scarf, which is selected to coordinate with whatever I am wearing. So this is not a "transfer" item.
Umbrellas: I have a ton of them everywhere so I am never without. I keep one in my laptop bag. A few in my car. And several in the coat closet.
There is always that moment when I am standing over the trash can cleaning out old kleenex and ticket stubs and gum wrappers and other junk left in my purse from the prior use. If I'm running late, I do this later, but it drives me nuts so first chance I can get you'll find me doing the de-clutter/dump... public restroom... gas station... work trash can..