Locks
I have a set of about 6 keyed alike smaller (but big enough to be somewhat stout) locks and I carry one on each motorcycle along with about 18" to 24" of kind of light duty (but welded) chain. I put the lock on the end of the chain and then put the whole works in an old athletic sock just to keep it all kind of together and keep it from scratching anything. This gets small enough so that it can be stored away on almost any bike SOMEWHERE. The nice thing about the lock and chain is that it is not stiff at all, but can be used to lock a jacket (or two) and helmet (or two) down to the bike just to keep honest people honest. I just run the chain thru a sleeve and then through the helmet and lock it all down to where ever works on the bike. If some thief really wants your stuff, he is going to get it somehow. Not only does all that work, but it is pretty cheap if you buy the chain and locks at someplace like Home Depot.