My daughters, being in their 30's, are probably close to the age range most of the posters are concerned with.
I gave them a box full of knives, mostly BM's, of several different types, and told them to take their pick.
Both chose the BM625S, and BM612S, the Crawford Leopard and Leopard Cub, half serrated blade. They liked the appearance, ergonomics and function (this series has consistantly the best working liner lock of all BM types I have tested).
Another good choice for 'dress up' would be the BM 850S, the Mel Pardue 'gent's' (tell her it stands for gentleperson's).
As far as the seat belt issue goes, the best tool for that is trauma shears (the large plastic handled scissors with the blunt blades angled about 30 degrees at the pivot point). Keep a pair handy in all your cars.
These work better than a knife, as they require only gross motor skills to operate, and they will cut through belts like butter; they even will cut through sheet metal. Further, the blunt points prevent accidentally cutting the person being extracted.
A small pry (or 'J') bar is also excellent to have for smashing windows, and levering doors open.
Don't forget a flashlight. Have a MagLite in all your cars, and attach a Photon to her key ring. A 3 D cell MagLite will last about 16 hours constant on, and the Photon in green will last about a week, constant on.
Hope this helps, Walter Welch MD, Diplomate, American Board of Emergency Medicine, father of two daughters.