I have a 25 lb Harbor Freight aluminum jack that I have been beating on for 6 years. I like it so much I bought another. They go on sale for $59. But lighter and more compact is a used jack from another BMW.
I also throw a summer or winter wheel in the trunk on trips, though I do not leave it there all the time. A compact wheel would take up less space and I might buy one if I ever find a cheap used one.