It would be awesome if you could have all the tools you need with you when something goes wrong. This, though, will probably never happen. The best you can hope for is to have the tools you need to get your bike home and fix whatever is wrong. Here are some essentials you should have in the toolkit you keep on your bike at all times.
Other smart things to have on the bike at all times are a tire patch kit and a few extra light bulbs and fuses. Fuses and light bulbs can go out and are easy to fix. Having a few on hand is smart so you can quickly change them and stay safe on the road.
As far as tire patch kits go, there are several different kinds out there, but I prefer to use tire plugs. Here's an article on how to patch a motorcycle tire.