I'm pretty happy with the additional bits I've bought for the K2 to give a little added protection.

1. There is obviously the pinned comment re the screen protector by sgoldstein - https://support.hammerhead.io/hc/en-us/community/posts/1260801646509-Extra-layer-screen-protector

2. As Martin B commented in the below thread, a magnetic USB C cable acts as a fantastic rigid dust protector for the USB C port (much more rigid than the ones provided, and doesn't need to be removed for the charging), and also makes charging a doddle (the magnet is very strong in the one I bought!).

https://support.hammerhead.io/hc/en-us/community/posts/1260801830430-Micro-USB-rubber-plug-protection-Silicone-case

3. EDIT: TUFF LUV make a perfect case for the K2 which has proper padded buttons on side, and even mic holes on back.

4. Finally, I found a nice zip up case which fits it (with the garmin case, usb c connector and lanyard attached) perfectly. Very snug with no movement at all.

Photos:

Silicon Case, Screen Protector and USB C Connector

USB C Cable and Magnetic End

Carry Case

Thanks to all the posters listed above who made the suggestions I found included here for the first 3 items.

I don't know if HH wants people posting links so I'll give full descriptions in italics for you to copy and paste into Google and it should be at or near the top of the results.

Screen protector £6.89 (Amazon / protectionfilms24.com both provide 3 packs) - brotect Glasbrotect Glass Screen Protector compatible with Hammerhead Karoo 2 

Silicon Case £11.99 (Amazon) - Tuff LUV [Compaitble with Hammerhead Karoo 2]

Magnetic USB C Cable £12.99 (Amazon - the one I put here is 2 cables, 2m long with both ends USB C so wont go into a standard USB plug, needs a fast charging USB C plug - there are many variations available on Amazon and elsewhere) - NIMASO Magnetic Charging Cable【2M+2M】USB C to USB C Cable 60W 3A Magnetic Charger Cable PD Charging Lead for Samsung Galaxy S20 Ultra/Note 20 Ultra 5G/S21 Ultra,iPad Pro 2020,MacBook,Google Pixel4

Carry Case £5.99 (Ebay - sold by "plannas" arrived within 3 days - may need to search on ebay rather than google) - Hammerhead Karoo 1 Karoo 2 Carry Case Bag.

Hope this helps K2 users!