Once witnessed an event where a jogger (whose dog wasn't on a leash) kicked a rottweiler (that was on a leash) because it was "threatening his dog". The rottweiler didn't even seem to notice that he'd been kicked. That guy really put his weight into it, too! ...the rottweiler's owner then turned it loose to chase the other dog and kicking jogger away. I thought the event was comical. Thinking about it again now still makes me chuckle. You can't imagine the look of surprise on that jogger's face when his foot landing on that rottweiler went completely unnoticed (except by the owner).
I've never really had a problem with dogs, but I think that if I'm being chased by a big dog like that, the best solution is to ride away as quickly as I can!
As to the original post: I carry water, a mobile phone, and maybe some cash or my wallet.