a way to select everything on the canvas and then tell all the hexes to Snap To The Grid on their own?
Oh my gosh, wouldn't that be an awesome feature?!! I might have to make an official request for that. But it doesn't exist now.
Since you're using hexagons, I would just snap one hexagon to the grid. Then hide the grid, and from there on, snap to the existing hexagon. And snap the next to those. If you keep the grid always visible, you'll need to be zoomed in enough to make sure that it snaps properly. Or else pay attention to the notification, that it always says "node to grid intersection".
Also, I don't know if this has been fixed. But there's always a rectangular grid in a file. And in Document Properties > Grids, if you only hide the grid, things will still be trying to snap to it. So you have to completely disable the rectangular grid, to prevent things from trying to snap to it. I know, it seems crazy to me that anyone would want to snap to something they can't see, but Inkscape at least used to work like that, and it might still. So be sure that the rectangular grid is disabled completely.
Inkscape also will try to snap to things in a hidden layer, so sometimes the only way to control snapping is to be zoomed in and watch the notification, to make sure it happens like you want.
I see that you're using a smaller computer screen. There are some more snap settings that you can't see. At the bottom of your snap control bar (far right edge of the window) see the tiny triangle? Click on that, and it shows all the rest of the buttons, except they are in a menu format. Click and click again to toggle, and you can see the checkmark indicating that each option is enabled or not.
For this project, I would set the snap control bar like this attached (where you can see the rest of the buttons, that aren't showing on your screen).
snap-basic.png
(5.32 kB . 30x583)
(viewed 255 times)And for Document Properties, I would switch Snap to Guides and for Snap to Objects, to Closer than 20 or 30 px. That means that you need to drag a new hexagon closer than 20 or 30 px, before it tries to snap. For Always Snap, Inkscape will try to snap it from anywhere. So if everything is set for always snap, it's a little like chaos, trying to control it.
There's another little trick that I use to help control snapping. Inkscape Preferences > Behavior > Snapping > Only snap the node closest to the pointer. And put the slider around 0.8.
With that, you always grab the object near to the node that you want to snap. That helps to prevent everything trying to snap to everything.
Keep on practicing - you'll get there!