Howzit Hilo!
As someone who collected bottles in Hilo I understand all about earthquakes. I used to lose about half my collection in every big quake back in the 70's
I was just a kid back then and didn't really care that much - I'd just go out and find more
When I moved to Northern California I didn't escape the earthquakes. However, I became much smarter in my displays and haven't lost any more bottles - even in the magnitude 6.9 Loma-Prieta quake
I assume that you're still in Hilo, otherwise you don't have an issue. A big quake on Oahu is around magnitude 4. That won't even knock a bottle off the shelf!!!
Here's one suggestion for your display: Secure 2x4 lumber directly to your walls. They should be screwed directly into the studs. A 2x4 is about 3 1/2" wide, so it will provide plenty of width for a soda (approximately 2 3/8" wide). Attach as many (and as long) as you need for your collection.
Now, the best way to describe my idea is to think of each display section as a "box". For safety, the inside of each box should measure about 19" long by 10" tall. This is big enough for 8 sodas to fit tightly packed, side by side (go a bit over 19" long for marbles and Hollister squats - of which I see you have both).
Each box should have 3 wires accross the front to keep sodes from falling out during a quake. As measured from the surface the sodes sit on, these wires should be placed at 2", 4" and 6". The 2" wire keeps sodes from rolling underneath (since they're 2 3/8" in diameter). The 6" wire should be high enough to keep them from leaping over the top.
You can run a couple of 2x4s accross your wall at about 5' and 6' height (best for viewing) and use vertical peices to create the separate "boxes". Note: if you choose to make longer boxes it increases the possibility that your wires will not be able to hold your bottles during "The Big One". My old bottlin partner from Hilo (who now lives in Kona) found this out when his fishing line failed during the big Kona earthquake. He lost over 100 sodas that day, don't make his mistake!
Here's a picture of my quake tested setup in Boulder Creek California (long since dismantled). Note: it's not exactly what I described and it uses a 4 wire technique. I used a cabinet that was already in the cabin and bolted it to the wall. The 4 wires accross the front are iron tie wire available in any hardware store. You'll probably want to use something more aesthetically pleasing like heavy duty (stainless steel preferred) fishing line
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My son Justin has more bottles displayed than I do. 
I changed my priorities and decided to do the things that I love and to try to get my son interested in my hobbies as well. Its been working so far.
