I use a willie & max toolbag on my forks - I like the look but you'll find that any bag that attaches to the lower yoke sorts hangs awkwardly from it, like this:

You could also hang it from the lightbar if you have one, but that'd hang even worse.
To make it sit right you need a right-angled bracket that bolts up under the lower yoke to the driving light mounts, and sits behind the bag to hold it slightly away from the forks. Then it sits like this:

That also has the added benefit that you can bolt it directly to the bracket instead of using straps round the yoke, so that even if someone steals your tools, at least they can't steal your bag (easilly), and it's a lot less likely to fall off in transit. It's also a lot easier to clean your lightbar without the bag in the way.
Matt