Ah, I have indeed been in these situations as well, particularly with the hair under the purse strap thing, once or twice or ten times in the car door, but never in a tree!  lol  I'm just a bit past BSL with basically straight, but slightly wavy hair, and unfortunately I rarely let my hair down anymore, just for these reasons.  Usually a simple bun or hairsticks does the trick, but when I have time I like to get more creative with pulling my hair up.  When I do leave it down I'm very careful to sweep my hair to the right as my purse strap goes over my left shoulder, which doesn't always do the trick anyway.  And getting in a car, especially on a windy day, I pony tail up my length just using my hand until I'm in and the door's safely closed....when my hands are free that is.  I also must be careful when I'm wearing my hairsticks and getting in the car, never fails, they always get hit on the way down, sometimes knocking them out and ruining the 'do, other times just pulling my hair and hurting like the dickens!