Hiya, from another fibro sufferer.
I find that a 'border' fork and spade doesn't jag the back and fibro as much as 'regular' sized. Though we're trying to turn over to all 'no dig' gardening now we've tamed most of our jungle. ::)
ALWAYS keep warm enough! (especially around lower back and neck) if you're affected by the wind.
In the shed, a supply of instant coffee sachets (you'll be taking flasks with you I presume, or have a brew kit on site). I also have a warm blanket for when the neuro-fatigue hits.
In your gardening kit, enough painkillers to fell a small army, lol
have a great time in the 'Green Gym'.
Camo