I like to be prepared. Thus, I've spent decades hunting down the perfect compact umbrella, sewing kit, hair brush, hair dryer, COMPLETE make-up kit (Hard Candy's "Take Out Makeup Kit"--out of production, but if you can find it, buy several: "Open wide to find a built-in mirror and six Super Shine Lip Glosses. Flip to the next level for eight Eye Candy Shadows, a classic black eye pencil and black mascara. Finally, finish that face with two shades of concealer, a bronzer and a blush...all necessary applicators are included." Measurements: Height is 1", length is 3.5", and the width is 2"!!!; one of my favorite things EVER!), panties & nighty (can double as a bathing suit), pads, tampons, condoms, lube, discreet vibe (surprise, surprise), deodorant, perfume, first aid kit(with mini-pharmacy), emergency slippers or flip-flops, drinking cup, utensils, notebook, multi-colored ink pen, address book, wallet (the size of a clutch), checkbook (that doesn't fit in the wallet), gum, toothbrush w/paste, emergency 'meal bar,' lighter, cigarettes (I don't smoke, but there are few things more hellish than being stranded with a smoker who's out of cigarettes), sweater/shrug, lotion, disinfecting spray/gel, toilet paper (trust me on this if you ever travel outside the US), tissues, small towel, purse hanger, Swiss-Army type knife, manicure kit, flashlight, spare keys...and more I'm surely forgetting.
I also HATE to be bored if I'm stranded somewhere. Technological advancements have helped tremendously--cell phone, iPod, Kindle, Nintendo DS have replaced my old Walkman, audio cassettes, mini photo album, emergency contact book, dictionary, journal, copy of my favorite book, book of poetry, and whatever book I was reading at the time.
You should see what I define as an 'overnight bag.'