I haven't had a need for a jack yet, I change the oil on the side stand just fine (then just sit on it for a minute to make sure it all drains out.)
I've seen home-made jacks though by bolting a couple of 4x6's together in a stack, drilling a hole in one side, sliding them under a bike, then sticking a strong pipe in that hole and pulling back, effectively lifting the bike up on the 4x6's. I think I'll do that eventually if I ever have a need.