When going on a longer trip, I make sure to bring a bigger tote with enough room for lots of extra diapers, clothes, toys, and other cleaning items. A regular diaper bag with many pockets makes it easier to organize, but if you're a bag-lady like me, and still want to get use out of your beloved handbags, then the secret is to use packing cubes or bag organizers. I got these little zippered, mesh packing cubes from the dollar store, so everything I pack has a place and makes items super easy to find.
1 bag: balenciaga giant brief bag (discontinued)
3 Diapers: cloth diapers
2 outfits: sesame street onesies (discontinued) / pants (homemade)
5 toys: natural rubber paci / silicone teething ring / dad rattle and crinkle bear / black and white rings
2 items for mama: sunglasses / iphone