I previously made a J hook for metal detectors for the vertical part of the roll bar. They've been working great. https://www.thingiverse.com/thing:2355327
I used some bungees for hanging stuff from the horizontal top bar but it was difficult to hook and unhook items. After a series of 3 creation failures (PETG is very flexible) I ended up incorporating hook loop strips into this solution and is now working fine for getting items off the floor (more dog room). Easy to hook a strap for travel and unhook for use without needing a full reach in to manipulate both the hook and handle.
The canvas bag pictured is quite heavy. It destroyed the first version and didn't last long with a double thick version but so far so good with this thicker wider velcro strapped snug version. The little V plug helps keep the hook & loop straps securely mounted in the S-Hook body.
I used 3/4" double sided velcro/hook & loop strapping (~20mm). The V holds in place best if the rough/loop side of the strap is in contact with the V surfaces e.g. smoother side out. Once snugged into place for awhile the V plugs hold the strap in place for repeated open/close efforts.