I too usually use a bag of water softening salt... I just leave it in the bag it comes in (about 50 lbs.) and put it on the seat within another garbage bag....I use the seat belt to secure it and the stuffed bear that rides monkey. I usually do only tarmack with the goldwing so haven't ever had an issue with the weight shifting. The bag is easy to lift out when taking a passenger and cheap and easy to replace if it gets ragged. It is also easily attainable when I find myself away from home without ballast or a passenger. I have used small sandbags as well, but find they tend to shift a little more.