Motorboating! I sing scales while doing this to warm-up. Mostly for support exercises.
Also back to op:
I do not recommend your first three things, for these reasons:
1 - Laughing can actually cause you to damage your vocal folds if you are laughing too hard and for too long. (i've actually learned this the hard way and lost my voice a number of times because i've laughed for too long and too hard)
2 - Singing in the car, don't do this because you can't listen to yourself fully as to judge what you're doing because you should be focusing on the road (or you will be focusing on the road more) rather then focusing on proper technique.
3 - Screaming is bad for the same as reason number one, it's harmful for your vocal folds.
If you also are feeling as if you are forcing lower/chest tone, then don't...you should only be doing what is natural for yourself, this again can also lead to damage. Yes, to go lower you must relax your vocal folds, however; I do not recommend forcing anything.