Hi @synapseslouch,
I like @Lia's solution (even down to the access maneuver, which is something I used with my original Synapse [from the first production batch when there was only the smaller size] -- see, for example, @GEOcyle's
Synapse continues to surprise. thread from 2012 about accessing the side pockets). It may be easier for you to access the Synapse 19 side pocket from having the bag on your shoulder, but here's a section of the Pack Hacker video review of the Synapse 25 that shows the presenter swinging the bag across to access this side pocket (around 7:25 into the video review; I'm only posting the screen capture so you can scrub to the section of one way to access the pocket with the bag on your shoulder):
This is from the video review at:
https://packhacker.com/travel-gear/tom-bihn/synapse-25/ . where the sequence starts around 7:25 into the clip.
However, I'll offer some alternative suggestions/modifications that can either help organize the side pockets along the lines of her suggestion and/or help to contain your keys (along the lines of suggestions made by both @carrot and @yvandermeer) if you are looking for ways to keep your keys from tangling with other items in your pockets or main compartment and getting lost (although the cleanest solution would be an organization scheme that still lets you keep them at the end of the keystrap)
It's most usually the side zippered pockets where you can improve the organization, and in addition to Size 1 Travel Stuff Sacks, I would most particularly recommend the Small Ghost Whale Organizer Pouches (GWOP) for recent accessory additions that are particularly good for organizing the Synapse side pockets. Here are some options for controlling your keys with small accessories:
These are Color Zipper Ghost Whale Organizer Pouches and a Mini Q-Kit
Mini Spacer Mesh/Ultraviolet Zipper, Super-Mini ScrapBlack/Iberian Zipper, Mini Q-Kit Kiwi (retired color)
Here's an overview with a few different sets of keys:
Closeup views:
Closed up with keys inside these are very flat
From your initial post, I wasn't sure whether you wanted to use the main compartment of the Synapse 25 for tethering your keys, but just wanted a way to keep the end of the keystrap from falling down where it couldn't be recovered. One way to solve this is to use the fact that your Synapse is filled with paper, folders, etc. but move the tether point so that you're not using the O-ring that drops your keys behind your cache. I've indicated the location of that O-ring by tethering a (retired color) 16" solar keystrap to that O-ring at the left.
You can use the same webbing loops that are used to suspend your laptop's cache with rails to tether your keystrap. What I've done here is to hook one loop of a medium size double carabiner clip into this webbing loop.
At this point, you have a lot of options: you can choose to tether a regular keystrap to the double carabiner clip (either to the metal opening or to the loop itself). It may not be obvious from the picture, but if you go back to the earlier picture of the Ghost Whale pouches and Mini Q-Kit with keys, and see a Wasabi double carabiner clip, you'll see an Iberian Split-Ring keystrap with a snaphook that can slide along the Double Carabiner Clip loop. This is because the surface of the clip (a hardened material that is not plastic) is both smooth, and slightly flattened.
So, you could tether the snaphook of a keystrap to that Double Carabiner Clip (and shift the tether position so your keys are unlikely to fall down the side of your bag where you have to grope through and disentangle them). You could lay part of the key strap over the adjacent carabiner loop, to get more control of the keystrap position. You could tether one of the Ghost Whale Organizer Pouches in the Super Mini or Mini sizes that are holding your keys directly to the Double Carabiner, or you could tether them to the end of a keystrap that ends in either an O-ring or a larger metal Split Ring that is hooked to the Double Carabiner.
All of these variant solutions still put your keys in the main Synapse 25 compartment and out of the way of the side pockets, water bottle, and bottom pocket where you're finding insufficient room. It also makes use of the fact that your Synapse is loaded with papers to make the keys or pouches sit on top of this load.
Here's a closeup shot of how you might tether your keys in the Mini GWOP to the Double Carabiner:
Attachment 23929
You also have the option of using the Ghost Whale Organizaer Pouches or Mini Q-Kit to keep your keys from sprawling and put them into a side, bottom, or center pocket. If you do want to organize the side pockets, I'd suggest the Small Ghost Whale organizer pouch is likely to be the most useful size for that pocket, since it is well shaped for the narrower side pockets and is about the size of an eyeglass case (but has 3-dimensional capability).
You can also combine this with some kind of retracting key fob, as suggested in previous posts.
Finally, although the Double Carabiner Clips won't be on sale separately until early next year, you can still get one of these (in Wasabi Green) free, if your order contains any
Knitting Tool Pouches I've linked you to the Size 2 Knitting Tool Pouch which I use to store my computer connectors (reinforced ballistic nylon ends help here; this pouch is also good for cutlery for the same reason; it can also be used as a shorter pen/pencil pouch if you want to put an A5 notebook into an A5 size Ghost Whale Organizer Pouch).
If you happen to order any of the new Handy Little Thing pouches, a pair of Double Carabiner Clips are included
HTH
moriond
ETA:
Hi @bluedawg,
I never used keystraps until I got my first Tom Bihn backpack, which was the (original)
Buzz Sling Backpack If you look at the Sapphire (redesigned) Buzz photo in my post, you can see the pen pockets in the front section are angled. That's because the sling format was designed to let you swing the backpack around without taking it off your shoulder and unzip the front compartment. The angle for accessing pens, etc. and the keystrap was exactly right -- all without taking the bag off your shoulder. We had forum members reporting that this design made it possible for them to use that backpack easily even when they had their leg in a cast and were hobbling around on crutches. I still have this backpack, which predates the first Synapse.