I used to just take ad-hoc bits, but after I found myself short of kit on the trail, I put together a bundle that I can grab without thinking. I have posted this before, but this is my back-pocket kit:
(USB stick is for scale!)
This little bundle would get me through most basic trail-side problems. It contains:
Topeak Mini 20 Pro (I love this tool. Certainly the best I’ve owned)
CO2 (x2) + inflator)
Patches + glue
Spare chain links
Odd bits of plastic (for fixing slit tyres)
Brake pads
Cable ties
Tyre levers
Valve adapter
(The neoprene sleeve was from eBay for a couple of quid. I keep the tool and kit separate to distribute weight in my pockets.)
In addition, I have a spare tube strapped to the frame (or in the back pocket on the road bike), but this is what I would take on a normal day out. If going longer or further, or if I’m with a larger group, I’d probably take a rucksack with first aid kit, extra layers and emergency blankets, spare inner cables etc, but for a normal day-trip, this is all I take.
Interested to hear what others consider to be mandatory trail kit…