@SomeGuyRides had a small Apache case bolted to his front rack. Johnny Pow had a small dry bag bungied to his. I thought about putting the toolkit there, but the toolkit is heavier than I'd want to have with that weight up front. Anything light and something you'd want to keep your eye on seems like a good choice. Bicycles have a similar front bag that can be purchased and common items are a hat, extra gloves, paperwork, sunscreen, snacks, wallet/money, etc. Something I'd have to seriously think about, particularly with that Motoskill rack, is that the front bag usually comes off the bike and with the rider on a bicycle, so something that can be quick release removed and taken with the rider has serious potential to be a grab-and-go bag.
Ortlieb has a waterproof front bag that goes with
this mounting bracket to achieve that result, for example. There's
a DIY version that you can make with
a quick release harness that could also be made a little fancier. Lots of possibilities.
For the center rack,
there is a dedicated mid-bag that you can buy. Again, SomeGuyRides and J-Pow both had tank bags they modified to go into that space. I don't think you could use it for while-riding nav with a full face helmet at least, because the bottom of the helmet would mean you would have to look VERY far away from the roadway to see what you're doing. I think if there was a lockable case that fit in the mid-space, that would be a very viable option for stashing a toolkit there that's left on the bike semi-permanently. On my bicycle I have a
bidon style tool carrier which is mounted to the underside of the downtube serving the same purpose.
EDIT: on the subject of the front bag - with the suspension being soft on the front, you'd think that electronics would probably fare well on the front bag. It's 50-50 from what I've heard; the shaking and vibrations are enough to kill some small electronics, to the point that maybe you don't want to stash a drone there, but some people have and it worked out ok.